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Globose； 3。5 to 7。5 cm。 in diameter； simple： tubercles conical； from a 4…angled base； lower ones short （4 to 6 mm。）； upper flower…bearing ones longer （10 to 12 mm。）； terete and grooved： radial spines 16 to 24； somewhat recurved from a bulbous compressed base； stiff and pectinate； horny or whitish （at length ashy）； interwoven with adjacent clusters； those on lower tubercles about equal （6 to 10 mm。）； on flower…bearing tubercles elongated； mixed with a few stouter ones and fasciculated （lower ones 10 to 12 mm。 long； upper ones 12 to 18 mm。 long and forming an apical tuft）； centrals none： flowers over 5 cm。 long and about 6 to 7。5 cm。 in diameter when expanded； bright sulphur…yellow： fruit ovate and green； about 12 mm。 long： seeds compressed； brownish smooth and shining； 1。8 mm。 long。 （Ill。 Cact。 Mex。 Bound。 t。 11） Type unknown； that of M。 pectinata Engelm。 is the Wright material in Herb。 Mo。 Bot。 Gard。
Extending from the hills along the Lower Pecos to El Paso； southwestern Texas； southward through Coahuila and San Luis Potosi to southern Mexico。
Specimens examined： Texas （Wright 226 of 1849； also of 1852； Evans of 1891）： Coahuila （Palmer of 1880； Mrs。 Nickels）： San Luis Potosi （Parry & Palmer 265； Eschanzier of 1891）： also specimens cultivated in St。 Louis in 1853； in Mo。 Bot。 Gard。 in 1892； and in Harv。 Bot Gard。
Even in the absence of the type I have ventured to refer Mamillaria pectinata Engelm。 to this species。 Dr。 Engelmann had concluded that the two were 〃not sufficiently distinct；〃 and the examination of Mexican forms which pass as C。 radians abundantly confirms this conclusion。 Besides； every character in the original description of C。 radians applies exactly to these Mexican plants and to our Texan specimens as well。 Aside from the fact that the Mexican specimens are apt to be more robust； I can discover no difference whatever。 For discussion of relationships see under C。 scolymoides。
46。 Cactus radians pectenoides； var。 nov。
Differs in its cespitose habit； fewer （16 or 17） and stouter spines （8 to 9 mm。 long）； and its larger and longer （10 mm。） less deeply grooved tubercles。 Type in Herb。 Coulter。
San Luis Potosi。
Specimens examined： San Luis Potosi （Eschanzier of 1891）。
47。 Cactus corniferus （DC。） Kuntze； Rev。 Gen Pl。 260 （1891）。
Mamillaria cornifera DC。 Rev。 Cact。 111 （1829）。 Mamillaria impexicoma Lem。 Hort。 Monov。 Cult。 5 （1839）。 Mamillaria cornifera impexicoma Salm。 Cact。 Hort。 Dyck。 20 （1850）。
Globose； 7。5 cm。 in diameter； simple： tubercles oblong…ovate； 2 cm long； crowded； the younger axils woolly： radial spines 15 to 26； rigid and horny； curved or sometimes straight； reflexed； bulbous at base； yellowish （whiter with age） and with dark tips； very sharp； 10 to 12 mm； long； the central one much stouter； darker； slightly deflexed； 12 to 16 mm long； sometimes wanting： flower unknown： fruit obovate； red； 2 cm long： seeds reddish； angular； smooth； 2 mm。 long。 Type unknown。
From San Luis Potosi to southern Mexico。
Specimens examined： San Luis Potosi （Parry of 1879； Eschanzier of 1891）： also specimens cultivated in Mo。 Bot。 Gard。 in 1892； growing in same garden in 1893。 Mamillaria impexicoma Lem。； afterwards reduced to a variety； was based upon fewer radial spines and no central。 As the central is occasionally wanting in connection with the most numerous radials； and present with the fewest； such a form would have to be separated solely on the absence of the central spine； and even in the original description of impexicoma the central spine is only said to be 〃sometimes wanting。〃 It has been impossible for me to separate the forms。 It should be said that the fruit and seed characters given above were taken front a specimen whose few radials and no centrals would undoubtedly refer it to impexicoma。 As yet we are ignorant of the flower of C。 corniferus。 For discussion of relationships see under C。 scolymoides。
＋＋ Central spines 1 to 4。
48。 Cactus scolymoides （Scheidw。） Kuntze。 Rev。 Gen。 Pl。 261 （1891）。
Mamillaria scolymoides Scheidw Allg。 Gart。 Zeit。 ix。 44 （1841）。
Globose or ovate； 5 to 7。5 cm。 high。 subsimple： tubercles conical； 10 to 16 mm。 long； the upper elongated； incurved and imbricate： radial spines 14 to 20； straight or often recurved； white or horny； 10 to 20 mm。 long （the upper the longer）； central spines 1 to 4； longer （18 to 32 mm。）； more dusky； curved； the upper ones turned upwards and intermixed with the radials； the lower one stouter； longer； and curved downwards： flowers 5 cm。 long： fruit unknown。 Type unknown。
From the Pecos River； western Texas； westward into southern New Mexico； and southward into Chihuahua and San Luis Potosi。
Specimens examined： Texas （Hays of 1858）： New Mexico （Bigelow of 1853）： Chihuahua （Wislizenus of 1846）： also specimens cultivated in St。 Louis in 1858。
Specimens collected by Mrs。 Anna B Nickels across the Rio Grande from Laredo； Texas； and showing neither flower nor fruit； seem to intergrade between C。 scolymoides and C。 scolymoides sulcatus。 The habit is that of the former； the tubercles are those of the latter； while the spines are somewhat different from either。 The number of central spines in these specimens is very hard to determine； as on the adult tubercle they all assume a radial position。 The usual adult arrangement is an apparent absence of central spines； 10 to 12 rigid； spreading and more or less recurved radials （increasing in length from the lowest）； which are mostly white or the upper more or less dusky； and above； just behind the radial row； 2 or 3 stout recurved…ascending spines； which are white with tips more or less reddish…black； one of the spines usually much stouter and longer than the others。 This form may represent a distinct species； but it seems very unsafe to add species to the C。 scolymoides group without the fullest information。
Prince Salm…Dyck refers C。 scolymoides to 〃M。 daimonoceras Lem。 Cact。 gen。 nov。； p。 5；〃 but no mention of such a name can be found in the work referred to。 Labouret refers C。 corniferus to the same name and reference。 If 〃M。 daimonoceras〃 was anything more than a garden or herbarium name used by Lemaire I have been unable to find it； and Dr。 Engelmann's notes indicate that his search met with the same result。 It is possible that the name was applied loosely to this assemblage of closely related forms that seem to cluster about C。 corniferus。
A most perplexing question of relationship is presented by the forms that have been called pectinatus； scolymoides； sulcatus （calcaratus）； Echinus； and the Mexican forms radians； impexicomus； corniferus。 It may be that they are all merely varieties of one strong polymorphic type； but our knowledge of corniferus is so incomplete； and material of other forms is so scanty； that I can not venture to make such an assertion。 However； it seems probable that radians； pectinatus； scolymoides； sulcatus and Echinus all have green fruit； while in impexicomus and corniferus it is red。 It has also seemed proper to merge radians and pectinatus； also impexicomus and corniferus； and to refer sulcatus to scolymoides as a variety。 These seven forms are thus reduced at least to four species。
49。 Cactus scolymoides sulcatus （Engelm。）。
Mamillaria sulcata Engelm。 Pl。 Lindh。 246 （1845）； not Pfeiff。 （1848）。 Mamillaria strobiliformis Muhlenpf。 Allg。 Gart。 Zeit。 xvi。 19 （1848）； not Scheer （1850）。 Mamillaria calcarata Engelm。 Pl。 Lindh。 195 （1850）。 Cactus calcaratus Kuntze； Rev。 Gen。 Pl。 259 （1891）。
Differs in its smaller size； proliferous and much more cespitose habit； the dilated base of the more spreading tubercles； fewer （8 to 12） radial spines； usually a single central spine （wanting in young plants） and somewhat larger flowers。 （Ill。 Cact。 Mex。 Bound。 t。 74。 fig。 1； seeds） Type； Lindheimer of 1844 in Herb。 Mo。 Bot。 Gard。
Texas； from the Brazos to the Nueces。
Specimens examined： Texas （Lindheimer of 1844； Fendler 34； Wright of 1850； 1854； 1857）： also specimens cultivated in St。 Louis in 1845； 1848； 1853； 1859。
This seems to represent the northeastern extension of the species； and doubtless it will be found merging into it south and west of the Nueces。 Curiously enough one of the prominent distinctions originally given was the single central spine； while in the type specimen there occur tubercles with more than one central。
50。 Cactus echinus （Engelm。） Kuntze； Rev。 Gen。 Pl。 260 （1891）。
Mamillaria echinus Engelm。 Syn。 Cact。 267 （1856）。
Globose or subconical； 3。5 to 6。5 cm。 in diameter； simple： tubercles terete； conical； grooved above； 10 to 12 mm。 long： radial spines 16 to 30； pectinate； straight or little curved； rigid and appressed （interwoven with neighboring clusters）； ashy…white （often dusky at apex）； 8 to 12 mm。 long； the uppermost longer （12 to 20 mm。）； central spines 3 or 4； the upper ones turned upward and intermixed with the radials； the lower one very stout； 15 mm。 long； subulate from a very thick bulbous base； straight （rarely slightly curved） and porrect （deciduous in old specimens）： flowers 3 to 5 cm。 long： fruit oval； elongated； about 2 cm。 long； green： seeds elongated…obovate。 brown and smooth； about 1。8 mm。 long。 （Ill。 Cact。 Mex。 Bound。 t。 10） Type；