381 
eastward throughout its southern borders; horizonthalonius, intertextus, 
and dasyacanthus are confined to the very usual narrow northern exten- 
sion between the Pecos in Texas and the Upper Rio Grande in New 
Mexico; longihamatus, brevihamatus, and scheerii are forms which belong 
to the region of the “Great Bend” of the Rio Grande; while wrightii, 
muhlenpfordtii, and terensis are found throughout the southern border 
of the State, the first extending from EK] Paso to the mouth of the Rio 
Grande, the second from El] Paso to San Antonio, the third from the 
Pecos to the Colorado of Texas. The last three species, doubtless, 
have an equally wide east and west Mexican distribution. In opposi- 
tion to this usually eastern extension of Chihuahuan and Coahuilan 
forms, the three following extend westward from the Pecos-El Paso 
region into Arizona, the first reaching southern Utah: wislizeni, sinu- 
atus, and erectocentrus, From the low country of eastern Mexico setis- 
pinus and schottit reach the basin of the Lower Rio Grande, the former 
extending as far northward as the Brazos. 
The fifteen forms said to be restricted to the United States doubtless 
include some that are Mexican, and the statements here made are 
simply based upon the present record. Naturally the region of highest 
northern extension shows the greatest number of these peculiar forms, 
and such extension has evidently been most favored by the conditions 
of the Colorado basin, Nevada, Utah, and Colorado, having been 
reached through this avenue. The most prominent northern type is 
simpsont and its varieties minor and robustior, the species ranging 
through Colorado, Utah, and Nevada, minor being restricted to Colo- 
rado and robustior to Nevada, with a possible high northern extension, 
In the region comprising the southwestern corner of Colorado, southern 
Utah, southern Nevada, northern Arizona, and adjacent California, we 
find the largest display of forms that do not seem to have Mexican rep- 
resentation. In addition to the three already mentioned, there are 
xeranthemotdes, polyancistrus, whipplei, spinosior, pubispinus, johnson, 
octocentrus, and sileri, making eleven of our fifteen forms. Of the 
remaining four, hamatocanthus and brevispinus belong to the “Great 
Bend” region of Texas; viridescens is a form of extreme southern Cali- 
fornia, and the peculiar papyracanthus, restricted so far as known to 
New Mexico in the neighborhood of Santa I'é. The species orcuttii and 
limitus are as yet recorded only from the boundary between California 
and Lower Calfornia; but doubtless they with viridescens will be tound 
to have a Lower (alifornian distribution. 
5. CEREUS Mill. Gard. Dict. ed. 8 (1768), 
- Plants of various habit (globose to cylindrical, trailing, climbing, or 
erect), sometimes very large, with spine-bearing ribs: tlower-bearing 
areole close above fully developed spine-bearing areolw: ovary bear- 
ing scales which are naked or woolly and often spiny in the axils: fruit 
succulent: seeds almost without endosperm: embryo mostly hooked, 
