7 
same individual of D. gigas has no head, but a regular wide crescentic 
proximal articular surface. Below this on the posterior side is the large 
trochanteric fossa, which is bounded by lateral ridges, which are at first 
equal, but one soon exceeds the other in height, forming a trochanteric 
ridge a little above the middle of the shaft. The condyles are distinct 
from each other and are flattened below. One of them bears a robust 
longitudinal crest above, which makes it much larger than the other, and 
causes the groove that separates them above, to look outward, or to the 
side which supports the trochanter. 
Three of the species may be distinguished as follows : 
Vertebral centra much compressed, acute below; neural spines without 
PLOCESSES si oes casi e ys eee Vie ase hemaa oe Fest tana es Dz ineisivus. 
Vertebral centra less compressed, obtuse below ; neural spines without 
processes ; larger.......... iisleees oa Ho olebwiea viaweleanmses waaay D. gigas. 
Vertebral centra compressed, not acute below ; neural spines with cross 
PLOJECUONS shies ce moe ieicews vere we eaeene ees cesesovssscveeeD. cructger. 
DIMETRODON CRUCIGER Cope. 
American Naturalist, 1878, p. 830. 
This species is not uncommon in the Permian Formation of Texas. It is 
characterized by the enormous length of the neural spines of the lumbar 
vertebre, which form the dorsal fin seen in other species of the genus. 
They are found in masses adhering together like sticks or branches of 
bushes. In this species the spine sends off, a short distance above the 
neural canal, a pair of opposite short branches, forming across. At vari- 
ous more elevated positions there are given off tuberosities which alternate 
with each other. They form on several consecutive spines oblique rows. 
The spines are broadly oval in section, the long axis antero-posterior, and 
have a shallow groove on both the anterior and posterior aspects. The 
centra are elongate as compared with their other diameters, and are much 
compressed between the articular extremities, leaving a strong inferior 
median obtuse rib. Articular faces of zygapophyses oblique. Diapophy- 
ses short and robust, with large costal faces, and standing below the prezyg- 
hh fs : 
er Measurements. M. 
( antero-posterior ........-00. eee 048 
Diameter of centrum ~ vertical at end....... <b oe wists 028 
transverse at end........----0+ .030 
Elevation of posterior zygapophyses above centrum.... .025 
as _ cruciform process “ £6 sete’ 3008 
Expanse of posterior zygapophyses........+.-+- siete .084 
ne cruciform process..........- oi Saen Sapientustors -048 
, antero-posterior......... ee» .080 
‘Dinmoter obsping eb bese { LrAMSVCISC... ese. eens seeee 020 
antero-posterior.... .016 
“e 
. laa | transverse........- -016 
Length of several pieces of neural spines........ etic: <o1AO 
. 
