I'M PALAEONTOLOGY OF NEW YORK. 



at this point so that only the outline of .the spine can be detected. As it 

 occupies the position of the rostral plate, there may be room for question 

 whether this is not such a body, but with the present evidence, all indica- 

 tions are that it is a prorate spine coalesced with the carapace and thus 

 uecessarily existing on each valve. Below this spine the margin slopes 

 rapidly backward to the ventral edge, along which, for a short distance, it is 

 nearlv parallel to the dorsal line. The valve narrows backward, and at the 

 posterior extremity the margin is produced into an acute and slightly in- 

 curved spine, between which and the dorsal line the outline is strongly 

 incurved. The margin is very slightly elevated and appears to be broadly 

 infolded in the postero-ventral region, as in M. Oceani, the posterior spine 

 being a prolongation of this infolded margin or doublure. 



The Surface is smooth, slightly and evenly convex. The cephalic region 

 bears an optic, node distant from the dorsal line, and in its vicinity the cara- 

 pace has apparently been somewhat compressed over some irregularity in the 

 matrix. On the thoracic region is a faint longitudinal ridge, nearly parallel 

 to the dorsal line, which becomes obsolete toward the posterior extremity. 



Dimensions. The single valve measures 38 mm. in length, inclusive of the 

 anterior and posterior spines, and 16 mm. in its greatest width. 



Distribution. Hamilton group. In the Marcellus shales, on Mud Creek, East 

 Bloomfield, Ontario county. 



DlTHYROCARIS BELLI. 



Dithyrocarls Belli, Woodward. Geol. Magazine, p. 106, pi. in, fig-. 5. 1871. 



BlOiyrocaris Belli, Ethebidgb, Woodward and Jones. Fifth Rept. Committee on Fossil Phyllopoda of the 



Palaeozoic Rocks, p. (>. 18S7. 



Tins species was described from an extremely imperfect specimen in which 

 the valves of the carapace apparently overlap along their inner margins, only 

 their anterior portion being retained. The drawing shows two strong carinas, 

 but gives no indication of the hinge-line. The anterior extremity bears a short 

 spinule similar to that in the species Mesothyra (Dithyrocaris ?) Veneris, and the 

 surface is ornamented by abundant striae. 



Distribution. Middle Devonian. Gaspe, Province of Quebec. 



