CRYPTONELLA OF THE HAMILTON GROUP. 397 



Crjptonella? lincklseiii. 



PLATE LX. 



Terebratula lincklani ; Hall, Thirteenth Report on the State Cabinet, p. 88. 1860. 



" " Idem, referred to Cktptonella ; Fourteenth Report on the State Cabinet, 



p. 101. 1861. 

 Cryptonella linekleeni : Idem, Sixteenth Report on the State Cabinet, p. 44. 1863. 



Shell ovate or subelliptical, usually broader below the middle, varying 

 from moderately convex to very gibbous and sometimes subcylindri- 

 cal ; front rounded, subtruncate, or a little depressed. 

 Ventral valve varying from moderately convex to gibbous, somewhat 

 regularly urcuate in longitudinal outline, sometimes a little flattened 

 towards the front or marked by a narrow mesial depression. Beak 

 more or less abruptly incurved, and truncate by a foramen of mode- 

 rate size : umbonal slopes rounded or subangular, and concave towards 

 the cardinal margin. 

 Dorsal valve varying from moderately convex to gibbous ; the greatest 

 convexity about the middle of the Igngth, and thence curving regu- 

 larly to the sides and base. 

 Surface marked by fine concentric striae of growth, which are some- 

  times crowded together towards the front, causing a thickening of the 

 shell. Shell-structure distinctly punctate. 



The internal structure has not been determined, and I therefore refer 

 it with doubt to the Genus Cryptonella. 



This species presents some variety of form, from subelliptical to 

 broad-ovate. The length of a large individual is a little more than three- 

 fourths of an inch, with a width of five-eighths of an inch and a depth 

 of three-eighths ; while another form, which I refer to the same, has a 

 length and width of half an inch, with a depth of a little more than 

 a quarter of an inch. Some of the smaller individuals are a little more 

 than a quarter of an inch in length. 



This species is common in certain beds ; and for the most part is readily recog. 

 nized. In the less gibbous specimens, it resembles the O. jilanirostra, but the beak 

 is more incurved, and there is less angularity of the umbonal slope, while the 

 outline is more regularly rounded. In a crushed and distorted condition, it is not 

 readily distinguished from C. rectirostra. 



