Clarke — The Naples Faukta. 



Normal mature form. The mature shell has a body chamber extending 

 for not less than an entire volution. The normal form of the species is 

 discoidal, compressed laterally, with an evenly rounded venter and is well 

 expressed in figures 6 and 7, on plate 72, Palaeontology of New York, vol. v, 

 part 2. The whorl section in full-grown shells is, naturally, larger dorso- 

 ventrally in proportion to its width, than in earlier growth stages and thus 

 the more commonly occurring miniature specimens show a greater rotundity 

 of whorl. It is, of course, impossible to establish a definite expression of 

 the convexity of the whorl of the normal lorn, uniangulare ; the adult 

 itself may vary slightly in this respect, but there are extremes in this regard 

 which we have excluded from the species, designating them as distinct varieties. 



Development of the shell. The early history of the shell has been very 

 nicely worked out by Prof. C. E. Beeches.* So far as our material has 

 permitted we have reviewed and, in the main, corroborated these obser- 

 vations. Beecher's investigations were based upon pyrite specimens from 

 the Hamilton shales at Wende station, Erie county, X. Y., shells which, 

 after an examination of specimens kindly supplied by Mr. Beeciieu, we 

 regard as representing the variety compressum } as described more fully 

 hereafter. The nature of our material representing earl}' growth stages, 

 is mostly of a different and more fragile preservation, and some of the points 

 already established by the author cited, are not clearly expressed in our 

 barite replacements, particularly the course of the earliest septal sutures. 



Tin- ProtQCOnch. The primitive shell when placed in comparison with 

 the protoconchs of the other goniatites here described is distinguished by its 



87 88 89 90 



Figures 87-90. Tomocerai unianqulare. Views of the protoconch. Fig. 87. Side view ; figs 88.89, 

 views of the distal extremity ; fig. 90, view near the distal extremity, x 25. 



peculiar shape. Yiewed from its distal surface it presents a distinctly 

 triangular outline, the shell coming to a sort of blunt apex at the middle of its 

 extremity and sloping thence at the sides to the low, broadly curved venter. 

 This angulated contour of the distal surface is continued forward over the 

 rest of the protoconch but rapidly loses its prominence, so that the entire 



* On the Development of the Shell in the genus Tornoceran, Hyatt. Amer. Journ. Science, ut cit. 



