CHAZT LIMESTONE. 23 



36. 5. ATRYPA ALTILIS (n. sp.). 



Pl. IV. (bis). Figs 9 a, b, c, d. 



Rotund ; valves almost equally convex, rapidly attenuating from the middle to the beaks ; 

 beak of the dorsal valve small, acute, incurved over the other, which is closely appressed 

 to the dorsal valve ; surface of each valve marked by about 24 equal rounded radii ; eight 

 of the radii are slightly depressed upon the back of the dorsal valve, and much elevated 

 in front, meeting an equal number of slightly elevated radii of the ventral valve. 



This species occurs with the preceding, but is more rarely seen ; it is clearly distinct, and 

 readily identified by the more numerous radii, evenly rounded outline, and less angular 

 mesial elevation and depression upon the two valves. This species resembles, in many 

 points, the rotund forms of the higher strata. 



Fig. 9 a. View of the ventral valve, showing the beak of the dorsal valve. 



Fig. 9 b. View of the dorsal valve. 



Fig. 9 c. Lateral view of the same shell. 



Fig. 9 d. Front view, showing the elevation of the mesial radiL 



Position and locality. In the upper part of the Chazy limestone. Chazy, Clinton county. 

 37. 1. 0RBICULA1 DEFORM ATA ( n. 5p.) . 



Pu IV. (bis). Fig. 10. 

 Suborbicular, depressed ; surface smooth ; apex scarcely elevated. 

 Position and locality. In the higher layers of the Chazy limestone. Chazy, Cinton county. 



38. 1. MET0PT0MA1 DUBI A («.*;>.). 



Pl. IV. (bis). Fig. 11. 

 Oval ; apex, elevated, incurved ; surface nearly smooth, or with fine concentric lines. 

 Position and locality. In the lower part of the Chazy limestone. Chazy, Clinton county. 



39. 1. ILLiENUS ARCTURUS (71. *j3.). 



Pl. IV. (bi»). Fig. 12. 



Buckler rounded and narrow in front, thick, expanding abruptly towards its junction 

 with the first articulations of the abdomen ; subtrilobate, the posterior angles much extended. 

 A single articulation of the body only is visible ; posterior edge of the buckler nearly 

 straight ; eyes not visible, though their position is visible. The lateral lobes of the buckler 

 are wanting, or greatly compressed and contracted. 



This individual is the only specimen found, and further discoveries may make it necessary 

 to change the description to some extent. 



Position and locality. In fine semi-oolitic limestone at the base of the formation at Chazy 

 village. (State Collection. 



