I2 4 PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 
Remarks : Differs from C. lyelli in the subtriangular, shorter outline, 
the concave lunular margin, and the crenulations of the lower margin. 
As to the latter point, compare remarks above. 
Record of specimens : Mouth of Santa Cruz River, 4 right, 4 left valves. 
Distribution: Santa Cruz, Patagonian formation (v. Ih.). 
Affinities: C. plicatilis Deshayes (i860, p. 745, pi. 18, f. 6, 27) from 
the Middle Eocene of Paris comes near this species, but C. kokeni is 
narrower posteriorly, the surface markings are much more distant from 
each other, and the anterior dorsal margin is concave. Still more closely 
allied is C. sulcata (Sol.) (see Wood, 1871, p. 170, pi. 23, f. 11) from the 
Upper Eocene of England and France, which agrees especially well in 
sculpture, while the outline is more like that of C. plicatilis , although 
more produced posteriorly. 
48. Crassatellites quartus (Ortmann). 
PI. XXVII, Fig. 1 . 
1900 Crassatella quanta Ortmann, in: Amer. Journ. Sci., v. 10, p. 371. 
Shell ovato-elongate, comparatively thin, less convex than in the pre- 
ceding species, but more so than in C. lyelli. Apex only slightly promi- 
nent. Anterior end of shell rounded, posterior hardly angulated and 
hardly narrowed. Posterior dorsal margin straight near apex, anterior 
straight, only with a slight suggestion of concavity close to the apex. 
Surface ornaments as in C. lyelli , but the ridges more crowded, and a 
little less strongly developed. Ventral margin without crenulations. 
Measurements of Santa Cruz specimen : Length, 25 + x ; height, 1 5 
mm; of Lake Pueyrredon specimen: Length, 17 mm; height, 10 mm. 
Remarks: The single isolated valve from Santa Cruz is broken pos- 
teriorly, so that the complete length cannot be given. According to the 
lines of growth, however, we have here the following relations : Length, 
16 mm; height, 9 mm, which agrees well with the Lake Pueyrredon 
specimen, and would bring up the total length of the shell to about 30 
mm (not quite double its height). 
Record of specimens : Mouth of Santa Cruz River, 1 left valve; Lake 
Pueyrredon, 600' above base, 1 cast of left valve. 
