TERTIARY VERTEBRATA OF THE FATtM. 
'rurtlcs except Sj)liarijis, the only liviii" representative of the AthecaB. The bone, in 
fact, belongs to the most highly specialised type of swimming humerus, to which 
AVheland * has giveu the name parathalassic. The whole bone is strongly compressed 
dorsi-vcntrally. The head (Z>.), so far as preserved, is strongly convex and somewhat 
triangular in outline. The ulnar crest {a.) projects further beyond the head than 
in Psephophorus scaldil or in Sp)hargis. Between the anterior thickening, which 
terminates on the head, and the posterior border the surface of the shaft is concave 
Test-fig. 87. 
Left humerus of Psephoplwrus eocmms, type specimen : dorsal and ventral views, 
a., ulnar crest ; h., head ; c., radial crest ; d., entocondyle. I nat. size. 
on the upper and lower faces of the bone, but the ventral concavity is deepest. The 
part of the bone above the radial process is considerably more elongated in proportion 
to its width than in Psephoplwrus scald 'd and still more than in Sphargis. The radial 
prominence is very strongly developed, but it cannot be seen exactly what is the form 
of its ventral surhice, which, however, is not divided into two or more separate knobs, 
as in Psephoplwrus, and is continued on the ventral face of the bone obliquely back- 
wards, so that if the line of its direction were continued it would pass through the end 
of the ulnar process ; in both Sphargis and Psephoplwrus the ridge is placed more 
transversely. The dorsal surface of tlie shaft opposite the base of the radial process 
bears a deep oval pit for the attachment of muscle ; in Sphargis this seems to be 
represented by several smaller depressions. The dista,l end of the bone is incomplete, 
but, like the upper end, it seems to have been less expanded than in Sphargis. There 
is no trace of any ectepicondylar groove or foramen. 
On the whole, the bone resembles the humerus of Psephoplwrus rather than that of 
^ Amer. Journ. Sci. [4] vol. ix. 1900, p. 420. 
