Tropidoleptus Fauna at Canandaigua J,ak:e, N. ^'. 147 



Summary. 



The foregoing descriptions show that the general deduetions which 

 have been previously drawn as to the character of the nepionic shell, 

 the development of the pedicle tube and the deltidial plates, and the ac- 

 quirement of surface characters, hold good in the families here studied 

 for the first time. Other general facts will be noted under the families. 



Centrovcllida — The shape of Tii/^eria Icpida in the nepionic stage 

 is almost exactly that of adult Ccntrone/la, and thus another bit of 

 evidence is added to that afforded by the loop, showing its relation to 

 the Centronellidaj rather than to the Terebratulida^. Going back to 

 the very earliest stage, before the development of the dorsal sinus, the 

 shell has characters common to the superfamily, that is, a biconvex 

 shell with the ventral beak extended beyond that of the dorsal valve. 



TerebratiilidiV. — Runclla, in its early stages, is a rather simple, 

 generalized type of shell, not differing greatly from the very youngest 

 stage of Trigeria, but the development of its loop shows progress beyond 

 the centronelliform stage. The position of the first three punctae, which 

 is the same as that in the recent genus Teretnihulina, is interesting. 



Tcrchratellidce. — The evidence that Tropidoleptus belongs to this 

 family has not been strengthened or diminished by the present studies. 

 It still rests on the form of the loop as described by Hall, and later 

 verified by Hall and Clarke. The development is similar to that of 

 the Strophomenid^, and the articulation is like that in Ownetes. No 

 deltidial plates are developed, and the pedicle is probably functional 

 throughout life. The cardinal process is very large, and of a peculiar 

 type, (]uite different from that of any of the Strophomenidai. 



Spirifcridcv.. — The marked difference in shape and relative con- 

 vexity of valves of Cyrtiua in the early neanic stage, from Spirifcr and 

 DcltJixris in the same stage, together with the geological range, would 

 seem to indicate that, while both may be derived from the same ances- 

 tral stock, Cyrtiua is not a modified Spirifcr. Dfifhvris, Spirifer, 

 Atnbocadia and Cyrtiua all start out with an equivalve nepionic shell 

 and a pedicle opening shared by both valves. Eut with the first 

 changes in later nei)ionic and early neanic stages, when the fold and 

 sinus appear, Cyrtiua and Ambocadia become strongly inequivalve, 

 while in Spirifer and Deltliyris the valves retain for a short time their 

 equality of convexity. In other words, the generic habit is assumed 

 immediately after leaving the form that is common to all the members 

 of the superfamily, and Cyrtiua passes through no Spirifr-\\V.G. stage. 



