436 STUDIES IN EVOLUTION 



Besides the sutural and tubular development, the material 

 studied illustrates the inception and growth of the surface 

 ornaments, and as these features are rarely found, the princi- 

 ples involved are of more than generic application. 



The specific limits of T. uniangulare have not been clearly 

 defined, and many of the forms referred to Pcirodiceras ( Go- 

 niatites) discoideum Hall, are evidently of the former species. 

 A comparison of the type specimens of both with others 

 which have been grouped with them, as figured in the 

 Thirteenth Report, New York State Cabinet, and in Vol. V, 

 Part II, of the Palaeontology of New York, shows that the 

 first species is really the common one, and as far as known, 

 the second is represented only by the original types.* 



The adult differences are mainly noticeable in the depth of 

 the air-chambers and in the sutural curves. They can readily 

 be determined by strictly limiting the characters to those first 

 ascribed to each species. Parodiceras discoideum is also 

 apparently without the narrow cone at the bottom of the 

 annular lobe, and the ventral saddle is much less depressed. 



The material for this paper is a portion of a collection pre- 

 sented to the museum of Yale University by Thomas G. Lee, 

 M.D. The particular lot containing the Tornoceras consisted 

 of several hundred nodular concretions of pyrite of a radiated 

 structure, obtained from the Devonian (Hamilton) shales of 

 Wende Station, Erie county. New York. Most of them 

 preserved an organic nucleus, and about twenty-five species 

 have been identified as belonging to the Trilobita, Cephalopoda, 

 Pteropoda, Pelecypoda, Brachiopoda, and Crinoidea. 



Th« test of the trilobites and the shells of the brachiopods 

 are but little altered, while those of the cephalopods and 

 pelecypods are usually replaced by sphalerite, a difference 



* The following list is proposed as corrected references to T. timan(julare : 



\3th Ann. Rejit. N. Y. State Cab., 98, figs. 6 (bis) (type specimen) and 6? 



P'll. N. Y., V, pt. ii, pi. 71, figs. 11-14 (fig. 14=:type specimen) ; pi. 72, figs. 

 6, 7 ; pi. 74, figs. 2, 4 ; VII, pi. 127, figs. 10, 11, 12. 



Of these, pi. 71, figs. 11, 12, i;5 ; pi. 74, fig. 4 and pi. 127, figs. 11, 12, were 

 referred to P. ( Goniatites) discoideum Hall. 



