Raymond — Common Devonian Brachiopods. 289 



The first three of these differences point to an earlier acquisi- 

 tion of the characters through acceleration. The last would 

 tend to show that 0. chemungensis was in a progressive rather 

 than a retrogressive dine of development. 



Chonetes coronatus Conrad. 

 (Plate XVI, Rows 3, 4.) 

 Pal. N. Y., iv, 1867, p. 133, pi. 21, figs. 9-12. 



Chonetes scitulus Hall. 

 (Plate XIV.) 

 Pal. N. Y., iv, 1867, p. 130, pi. 21, fig. 4. 



Chonetes mucronatus Hall. 

 (Plate XV, Rows 4, 5.) 

 Pal. N. Y., iv, 1867, p. 124, pi. 20, fig. 1 ; pi. 21, fig. 1. 



Chonetes robustus sp. nov. 

 (Plate XVII, Rows 1, 2.) 



The New Species. — There are in the collection from Canan- 

 daigua Lake about 50 specimens of a Chonetes which differs 

 in important characters from any described species. The shell 

 is strongly concavo-convex, wider than long, with from 20 to 40 

 strong, sharp, equal striae which increase toward the front by 

 bifurcation and implantation. The umbo is smooth for a dis- 

 tance of from 1 to 2'5 mm , cardinal area of ventral valve narrow, 

 concave, and the delthyrium covered by a convex deltidium. 

 Pedicle opening minute, encroaching upon the ventral beak. 

 The posterior margin of the area bears from 4 to 6 pairs of 

 short divergent spines. For this species the name Chonetes 

 robustus is suggested. 



This species is more nearly related to Chonetes coronafaos than 

 to any other known brachiopod. It differs from it in the 

 smaller size of the adult, the much greater convexity of the 

 ventral valve, the fewer and coarser striae at the same stage of 

 growth, the smoothness of the umbos, the fewer pustules on 

 the interior of the dorsal valve, and the later emergence of the 

 first spines on the posterior margin. On the adult of this 

 species there are 6 striae in the space of 5 mm on the front, while 

 in C. coronatns there are 11. In convexity and size this species 

 resembles C. mucronatus, but is easily distinguished by the 

 sharpness of the striae and the angle of divergence of the spines. 



The figures on Plate XYII are all enlarged two diameters. 



Summary .— All the species in the collection have the same 

 type of changes in development ; hence they will be discussed 

 together. 



