CLUPEIDJE. 
139 
Genus DIPLOMYSTUS, Cope. 
[Bull. U.S. Geol. Surv. Territ. vol. iii. 187“, p. 808.] 
&yn. Histiurm, O. G. Costa, Atti Accad. I’ontan. vol. v. 1850, p. 288. 
Hyperlophus, J. D. Ogilby, Rec. Austral. Mus. vol. ii. 1892, 
p. 2(3. 
Head and trunk much laterally compressed, and abdomen com- 
pressed to an edge. .Maxilla robust and arched, with two supra- 
roaxillary bones ; mandible a little prominent, and gape not 
extending behind the anterior border of the orbit ; teeth minute or 
absent. Preoperculum only slightly expanded, operculum and 
suboperculum deep and narrow; branchiostegal rays about 10 in 
number. Vertebra; from 31 to 16 in numbor, the centra much 
constricted and strengthened with few longitudinal ridges. Paired 
fins of moderate or small size, the pectorals inserted above the 
ventral border, the pelvic pair either in advance of the dorsal or 
opposite its most anterior rays ; dorsal fin arising in front of the 
middle point of the back, nevermore but usually less extended than 
the anal, which is longer than deep ; caudal fin deeply forked ; no 
fin-rays excessively elongated. Scales small or of moderate size, 
not pectinated ; a series of thickened ridge-scales, not produced 
into lateral wings, extending along the back between the occiput 
and the dorsal fin ; a series of larger thickened ridge-scales, with 
lateral wings, similarly extending along the ventral border from the 
pectoral arch to the origin of the anal fin. 
Phis genus is represented at the present day by species from the 
'ivers of New South Wales and Chili. 
Diplomystus dentatus, Cope. 
1877. Diplomystus dentatus , E. D. Cope, Bull. U.S. Geol. Surv. Territ. 
vol. iii. p. 808. 
1877. Diplomystus analis, E. D. Cope, ibid. p. 809. [Nearly complete 
fish.] 
1884. Diplomystus dentatus, E. D. Cope, Vert. Tertiary Form. West, 
Book I. (Rep. U.S. Geol. Surv. Territ. vol. iii.), p. 74, pi. x. fig. 1. 
1884. Diplotnystus analis, E. D. Cope, ibid. p. 75, pi. vii. fig. 4, pi. viii. 
fig. 3, pi. x. fig. 2. 
J !/pe. Nearly complete fish. 
The type species, attaining a length of about 0 - 5, the caudal 
re gion comparatively slender but scarcely longer than the abdominal 
region. Length of head with opercular apparatus much less than 
the maximum depth of the abdominal region, which is contained 
nbout three times in the total length of the fish to the base of the 
caudal tin. Abdominal vertebra; about 18, caudals 23 in number. 
