808 BULLETIN UNITED STATES GEOLOGICAL SUKVEY. 



between the two genera are the small mouth in Dcqwdoglossiis, the ab- 

 sence of barbels, and the generally abbreviated form. From Arcqyaima, 

 it differs in proportions, and in the abnndance of teeth on the bones of 

 the roof and floor of the mouth. To this genus is no doubt to be re- 

 ferred the fish found in the Green River Shales which I called* Osteoglos- 

 sum encaustum, so that the name of that species will stand Daijedoglossus 

 encaustus. 



Char, S2)ecif. — Form oval, contracting subequally to the muzzle and 

 caudal peduncle. The front is gently convex and the mouth is terminal 

 The depth is little less than half the length minus the caudal fin, and 

 the length of the head enters the same 3.4 times. The dorsal fin is 

 shorter than the anal, and its first ray stands over the sixth of the latter. 

 The ventrals are small, and extend about one-half the distance from their 

 base to the first anal ray, which equals the distance to the base of the 

 pectoral. The latter is elongate, especially the first ray, which, although 

 jointed, as in Osteoglossum Mcirrhosum, reaches nearly to the end of the 

 ventral. Eadii : D. 22-23 ; A. 27-30. The caudal fin is slightly concave. 

 Scales five or six series above the vertebral column and seven below it. 

 Their exposed surface is rather wide, and is minutely granulated and 

 without grooves. . The cells are invisible except when this surface is re- 

 moved, and they are rather large. Vertebrte : 21 dorsal; 25 caudal. 



The orbit is rather large, and is reached by the end of the maxillary bone. 

 The suborbital bones are not much enlarged, as is the case in the recent 

 genera. Preoperculum entire; suboperculum very narrow. Branchio- 

 stegals slender, rather numerous; coracoid wide, forming a vertical 

 keel, which is not produced. Length of the longest specimen 0".230 ; 

 of the shortest, O'^.lCo. 



The five specimens of this fish which I possess do not differ widely 

 in size, and are one-third and less of the dimensions of the D. encaustus. 

 A scale of this or of another large species occurs in the present collec- 

 tion. 



DiPLOMYSTUS DENTATUS, geii. et sj). nov. 



Char. gen. — Family Clupeidce, and nearly related to the genus Clupea. 

 It differs from Clupea in the presence of a series of dorsal scuta, which 

 extend from the supraoccipital region to the base of the dorsal fin, cor- 

 responding in position with those of the ventral surface. Unlike these, 

 they have no costal processes. The dorsal fin originates in front of the 

 anal. In the typical forms, teeth are well developed in a single series on 

 the dentary, premaxillary, and maxillary bones; but, in the small forms, 

 they are invisible. Mouth moderate. 



There are two sections of this genus, the species of which differ in the 

 form of the dorsal scuta. In section I, these shields are transverse, and 

 their posterior borders are pec.tinate, a median tooth being especially 



* Annual Report U. S. Geol. Surv. Terr., 1370, p. 430. 



