152 NEW YORK STATE MUSEUM 



vomerine teeth in front, together with the deeply concave oral margin of 

 the lower dental plates. The functional surface of all the dental elements 

 is narrower than in Mylostoma, thus making some approach to Dinichthys- 

 like conditions, and a still further resemblance is to be observed in the form 

 of the vomerine teeth. The latter, if found in the detached state, might 

 readily be mistaken for the commonly so called "premaxillary teeth" of the 

 preceding family. The dorsomedian and other plates of the abdominal 

 armor are indistinguishable from those of Dinichthys. 



The unique specimen upon which this species and genus are founded 

 is extremely important for the light thrown upon the structure and relations 

 of the group to which it belongs, besides acquainting us with an interesting 

 connecting link between two well known genera of Arthrodires. Nearly 

 the complete dentition is presented for study, besides portions of the head 

 shield, suborbital, sclerotic ring, and several plates of the abdominal armor, 

 including a nearly perfect dorsomedian. All of these parts were inclosed 

 originally in a single block of shale; this has since been considerably 

 broken, allowing a number of plates to be disengaged from the matrix. 



The history of the specimen is as follows: collected in the year 1868 

 from an outcrop of Portage shale upon the farm of John Pierce, near Mount 

 Morris, Livingston co. N. Y., it was acquired for the Peabody Museum at 

 Yale by the late Professor O. C. Marsh. Here it remained for many years 

 stored away and apparently forgotten. At all events there is no record of 

 its consultation by any one prior to its being called to the present writer's 

 attention by Professor Charles E. Beecher, shortly before the unfortunate 

 loss to science of the latter. An opportunity for its description arising in 

 connection with the present report, it was generously placed at the writer's 

 disposal by his friend Professor Schuchert, of Yale, at whose suggestion 

 the specific title was inscribed to the memory of the lamented Beecher. 

 Although this specimen has already been noticed in the papers above 

 referred to, its importance warrants further detailed description. 



The dentition of this species presents features of absorbing interest. 

 The mandibles bear a superficial resemblance to the lower dental plates of 



