Raymond — Common Devonian Brachiopods. 281 



From the present material the writer has been enabled to 

 study the complete series of changes in 20 other species, 

 and a partial series in 4 more. This list comprises 15 

 genera, 11 of which are not represented in the work previ- 

 ously done. These genera belong to the families Centro- 

 nellidee (Trigeria), Terebratulidse {Eunella), Terebratellidae 

 ( Tropidoleptus), Spiriferidee (Cyrtina, Delthyris), Craniidse 

 (Pholidops, Craniella), Strophomenidse (Stropheodonta, Pho- 

 lidostrophia), and Productidse (Chonetes, Strophalosia). Cra- 

 nia, jRhipidomella, Spirifer, and Ort/wthetes are here repre- 

 sented by Devonian species, while the previous work has been 

 done on those from the Silurian ; interesting points may be 

 therefore obtained by comparing results. 



The present paper is an abstract of the results attained from 

 this study, and gives a summary of the most interesting facts 

 ascertained in regard to 17 of these species. 



Crania crenistriata Hall. 



Pal. N. Y., iv, 1867, p. 28, pi. 3, figs. 13-16. 



The smallest specimen of this species is 2'66 mm long and 

 3*33 mm wide. At the apex it shows the nepionic shell, which is 

 similar in form to the adult, but non-plicate. It is l*46 mm long 

 by l*66 mm wide. In this species, and in Craniella hamiltonim. 

 the young shells have, as a rule, more conical dorsal valves 

 than the adults. 



Stropheodonta inoequistriata Conrad. 

 (Plate XIII, Eows 2, 3, and 4.) 

 Pal. N. Y., iv, 1867, p. 93, pi. 12, figs. 6-8. 



Nepionic Stage. — In the nepionic stage the shell of this 

 species is oval in outline, and wider than long. Both valves 

 are convex, though in some specimens the dorsal valve becomes 

 flat in front. The latter valve bears a narrow median fold 

 which extends about half-way to the front. Otherwise the 

 shell is smooth. The length of the average specimen in this 

 stage is -42 mm and the width -54 mm . 



Changes during Development : Outline. — Immediately after 

 the nepionic stage the width at the hinge becomes greater than 

 that below, and remains so through all succeeding stages. The 

 cardinal extremities are most alate during the adolescent period, 

 and all immature forms are characterized, when perfect, by 

 long hinge lines. In the senile state, the cardinal angles are 

 not so extended, but the width at the hinge is still the greatest 

 width. (Compare the young specimens> Nos. 14 and 15 of the 

 series, with the adult and senile individuals on Plate XIII, 

 Kow 4.) 



