UPPEK TllIASSIU SPECIES. HJ 



ill i'unu, with the peripheral channel of somewhat varialjle depth, but usually 

 ^- ell- defined; volutions about five, more or less fiattened on the sides, round- 

 ing oft" a little to the periphery, and abruptly truneated, or even overhang- 

 ing on the und)iliral side, each enveloping about half of the next one 

 within; umbilicus rather shallow, or of moderate depth, and less than one- 

 third the diameter of the sliell. Surface ornamented by a variable number 

 of costas, which curve forward as they approach the periphery, often bifur- 

 cating once or twice in crossing the sides, and also increasing by the inter- 

 calation of shorter ones between, wdiile they usually bear on each side about 

 four or five rows of small nodes, the most i)rominent of which are generally 

 those along the margins of the peripheral furrow, and around the edge of 

 the umbilicus; the outer rows being slightly compressed, and more or less 

 oblique, while those on the sides of the volutions are apparently sometimes 

 obsolescent. (Septa not observed.) 



Greatest diameter of the largest si)ecimen seen (which is imperfect), 

 about 4 inches; convexity, 1.20 inches; diameter of umbilicus, about 1.15 

 inches. 



The specimen from which the foregoing description and our figures 

 were prepared, agrees much better with Mr. Gabb's fig. 12 than with his 

 fig. 11. He was probably right, however, in including both of his figured 

 specimens as varieties of one species, though I have not seen a, series con- 

 necting the two forms. Taking the specimen represented by hi.s fig. 12 as 

 the typical example of the species, our shell may safely be called T. Whitnci/i. 



Among foreign species, this may be compared with T. Archclaits, Laube 

 (Fauna der Sch. von St. Cassian, 5. Abth., pi xl, fig. 1); but it difters in 

 having its costcT more frequently bifurcating, with fewer nodes, none of 

 which seem to be developed into spines, as in I.aube's species. 



After 1 had written the foregoing, Pi-ofessor Hyatt sent me the follow- 

 ing note respecting it: 



■" This species is very distinct* on account of its coai-se i)i-ominent 

 nodes and pila;, the number of the latter, and the young, which are not 

 unlike the young of Gijmnotoccras Blalcci. The pilre of the young shell in 



*IIc means distiuct from T. Judicaricum ; lie conciured iu tlie opinion that it is 

 ihv T. Wliitncyi, Gabb (sp.j. 



