17 



extend beyond the margin in dentate projections; the smaller 

 generally commencing between the others about half way from 

 the apex. Ventral valve unknown. Length one-eighth of an 

 inch; width but slightly less. 



But one specimen has been found, which adheres to the 

 ventral valve of a Meristina nitida. 



CRANIA GRACILIS (N. Sp.). PL 2, fig. 7. 



Shell very much appressed; fragile, irregular in outline, with 

 a tendency to unequal lateral expansion; incurved on the poste- 

 rior margin. Apex acute, rising rather abruptly from the sur- 

 face of the shell, inclined a trifle posteriorly, position irregular, 

 nearest the incurved margin. 



Surface quite smooth, with very fine, concentric striae, which 

 are irregular in disposition as though the animal had built on 

 a part of the lip only at a time. Slope concave. Length of the 

 specimen from the posterior curve to the anterior margin three- 

 sixteenths of an inch. Breadth one-fourth of an inch. Ven- 

 tral valve unknown. Attached to the inside of the outer cham- 

 ber of an Orthoceras virgatum. 



This species can readily be distinguished from C. siiuriana, 

 Hall, by its extreme tenuity and flatness. 



CRANIA PANNOSA (N. Sp.). PL 2, fig. 8. 



Shell irregular in outline, spreading, appressed, slope concave. 

 Apex a small sub-acute, posteriorly situated, node, with a 

 smooth surface; which is but slightly eccentric in young shells. 



Surface covered by a rough epidermis with loose, very ragged 

 laminae that grow wider as they near the lip. Young shells 

 have a quite regularly concentric growth till they reach the diam- 

 eter of about one-eighth of an inch; when nearly all lateral 

 growth ceases at the posterior margin and continues by lateral 

 and anterior expansion. Diameter of the largest about one- 

 fourth of an inch each way. 



Three individuals were found on the exterior of the Orthoceras 

 in which the C. gracilis was attached. 



