40 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



versity Museum, shows the posterior portion of the cranium above and below 

 very satisfactorily. 



There is gf)ocl reason for believing that this species also occurs in the Hamil- 

 ton of New York State. Mr. F. K. Mixer, who has made a careful search for fish 

 remains in the •vicinity of Buffalo, has obtained certain fragments from the En- 

 crinal Limestone near the mouth of Eighteen Mile Creek, which exhibit almost 

 precisely 'the same style of ornamentation, and agree furthermore in size with 

 D. piistulosus. One of these fragments is identifiable as the suborbital plate, 

 and shows very distinctly the sensory canals. Another represents about one 

 half of one of the veutro-lateral plates, is rabbeted upon the edges, and shows 

 some variation in the size of its tubercles. Again we notice that tuberculation 

 of the ventral plates bears witness to primitive conditions. The ventro-lateral 

 measures 21 cm. in maximum width, and is traceable for about the same dis- 

 tance in a longitudinal direction, the remaining portion being broken away. 

 It is to be hoped that further and better preserved material will be forthcoming 

 from this horizon, since by reason of their greater antiquity and primitiveness 

 Hamilton Dinichthyids are likely to prove even more interesting than those 

 of Upper Devonian age. In the event of these plates being proved by future 

 discoveries to belong to a species distinct from D. pustulosus, with which they 

 are now provisionally associated, it is but fitting to reserve the name D. mixeri 

 for the New York species, in honor of the gentlemen to whom we are indebted 

 for our first knowledge of it. 



The title of D. pustulosus, although misapplied by M. Lohest for D. tubercu- 

 latus, has never been defined, and we are accordingly at liberty to appropriate 

 it for the present species. 



Formation and Locality. — Hamilton Limestone ; Wisconsin, Iowa, and New 

 York (?). 



In this connection a word may be said concerning another plate discovered 

 by Mr. Mixer, near Sturgeon Point on the shore of Lake Erie. The fossil is em- 

 bedded in a loose block derived apparently from the Portage Shale, exposures of 

 which occur at this locality. It presents the inferior aspect of a small dorso- 

 median plate, which is worn away anteriorly in such fashion as to reveal an 

 impression of the external surface. This is seen to be finely tuberculated, and a 

 few tubercles are left on an impression of a small plate (antero-dorso-lateral ?) 

 adjoining the first. The longitudinal carina and its terminal process are both 

 indicated, although the latter is partly fractured. The plate is quite thin ; 

 and this fact, together with its small size, fine tuberciilation, and other characters, 

 renders it probable that it belonged to an immature individual. It may be 

 referred with considerable certainty to D. ringuebergi, a species which until 

 the present time has rested upon a solitary dorsal shield from the same locality. 

 Mr. Mixer's specimen is about one fourth smaller than the type, however, 

 and is of more slender construction. If properly regarded as a young indi- 

 vidual, it is interesting as being one of the few that are known. 



