332 Annals of the Carnegie Museum. 



3. Ctenodonta ?bidorsata Raymond. (Plate XXIX, figures 4, 5). 

 Ctenodonta? bidorsata Ra\'mond, Annals Carnegie Museum, Vol. Ill, 1906, p. 577. 

 This small shell has something of the general shape of a Cte?iodo7ita, 

 and for lack of knowledge of what it really is, it is placed in that 

 genus. The specimen shown in figure 4 of the plate has somewhat 

 the appearance of a Pterotheca expanse, though it has no keel. 



Description. 



Shell small, longer than high. Hinge back of beak nearly straight, 

 rather long. End of shell in front of beak short and broadly rounded. 

 Lower margin gently curved. Posterior end short and rather acute. 

 The internal cast is marked by two narrow sinuses which radiate 

 from the beak. The distal end of the anterior one is nearly opposite 

 the beak, while the posterior one runs diagonally across to the pos- 

 terior-ventral angle of the shell. In front of the anterior sinus and 

 behind the posterior one there is a narrow ridge. The valves are only 

 slightly convex, highest at the umbo, and concave along the hinge 

 margin. One specimen is il mm. long and 7 mm. high. 



Locality. — A rare species in the trilobite layers of the Middle Chazy 

 at Sloop Bay on Valcour Island, N. Y. 



Family Ledid.e Adams. 

 Genus Clidophorus Hall. 



4. Clidophorus obscurus Raymond. (Plate XXIX, figure 9). 

 Clidophorus obscurus Raymond, American Journal of Science (Ser. 4), Vol. XX, 



1905. P- 372. 



Description. 



Shell small, longer than high, not very convex. Basal margin 

 nearly straight, anterior end rounded, posterior end narrow. In 

 front of the beak the cast shows a short clavicular impression which 

 extends about half the distance to the lower margin. The single 

 specimen is 6 mm. long and 4 mm. high. 



Locality. — Trilobite layers, Middle Chazy, Sloop Bay, Valcour 

 Island, N. Y. 



Family Cyrtodontid/E Ulrich. 



Genus Cyrtodonta Billings. 



5. Cyrtodonta solitaria Raymond. (Plate XXIX, figure 15). 

 Cyrlodonla solitaria Raymond, American Journal of Science (Ser. 4), Vol. XX, 



190.S. P- 373- 



