292 Raymond — Common Devonian Brachiopods. 



it is wider than long, projects little beyond the hinge line, and 

 is divided once. In the adult it is longer than wide, deeply 

 bifurcated in front, and quadrifid on the posterior face. (Com- 

 pare Nos. 3 and 6, Eow 3, with No. 12.) 



Tropidoleptus carinatus Conrad. 

 (Plate XVIII.) 

 Pal. N. Y., iv, 1867, p. 407, pi. 62, figs. 2, 3. 



Nepionic Shell. — In the nepionic stage, the shell of this 

 species is transversely oval to subcircular, with a hinge width 

 less than the width below. Both valves are convex and smooth. 

 In the early part of this stage the shell is distinctly wider than 

 long, but just before the inception of the plications the length 

 and breadth are about equal. 



Changes during Development: Outline. — In the earliest 

 neanic stages the shell becomes longer than wide, and this 

 form is maintained until the shell reaches a length of from 4 to 

 7 mm , after which the width is greater than the length. (Com- 

 pare the first ten specimens of the series with the last four on 

 Plate XVIII.) From the early neanic through the adult 

 stages the width of the shell at the hinge is greater than the 

 width below, and the cardinal extremities are usually mucro- 

 nate. In senile stages the width continues to increase without 

 a corresponding growth on the posterior margin, which pro- 

 duces rouiflded cardinal extremities and gives the shell a trans- 

 versely elliptical shape. 



10 9 



Figure 9. — Tropidoleptus carinatus Conrad; profile view, showing rela- 

 tive convexity of valves, x 9. 



Figure 10. — Beaks of another specimen, showing pedicle opening and the 

 wearing away of the ventral beak. x 6. 



Convexity of Valves. — Up to a length of from "75 to l mrn 

 both valves are slightly convex, with the pedicle valve some- 

 what the deeper. At this point, where the plications gener- 

 ally begin, the brachial valve becomes slightly concave, and 

 continues so through the later stages (figure 9). 



Plications. — Immediately after the nepionic stage plica- 

 tions arise on both valves, and apparently several are formed 

 at once. On an individual l-6 mm in length there are 10 plica- 

 tions on the dorsal valve and 9 on the ventral. ]STew plications 



