Raymond — Common Devonian Brachiojpods. 293 



are added at the sides and never implanted, nor do they ordi- 

 narily bifurcate. In the adult there are from 17 to 21. 



Gerontic Stage. — The senile characters in this species are : 

 Hinge width less than the width below ; strong varices of 

 growth numerous ; obliteration of the plications toward the 

 front of the shell. The plications become flattened and indis- 

 tinct toward the front of shells over 20 mm long. 



Cardinal Process. — The cardinal process is large and prom- 

 inent. It is joined in front to the bases of the crura and 

 between them is a thickening of the shell, forming a platform 

 which slopes forward to the floor of the valve. (See last figure 

 on Row 3, Plate XVIII.) The posterior face of the process 

 is smooth and rounded, and the lower third is covered by a 

 strong chilidium, which also bounds the posterior ends of the 

 dental sockets. The posterior wall of the cardinal process has,, 

 near the top, a narrow, rounded sinus formed by a shelly loop, 

 which is continued forward and downward till it unites with 

 the platform. On either side of this process is a deep conical 

 hole, which extends nearly to the apex of the shell and prob- 

 ably represents the place of attachment of the diductor mus- 

 cles. (See last figures on Rows 3 and 4, Plate XVTII. The 

 platform has been broken away from the specimen at the end 

 of Row 4, but the loop in the middle of the process and the 

 two holes are well shown.) 



Directly in front of the loop is a groove in the platform 

 leading back to a minute anal tube, which runs along the 

 middle line of the process and has its external opening in a 

 pore just at the point where the chilidium meets the apex of 

 the valve. 



Trigeria lepidct Hall. 

 Pal. N. Y., viii, pt. 2, 1893, p. 274, pi. 50, figs. 36-40. 



Description of Smallest Specimen. — The smallest individual 

 of this species is roughly triangular in outline, the rostrate 

 beak, which projects •25 mm beyond the hinge, forming the apex. 

 The ventral valve is convex and smooth, 

 without fold or sinus. The delthyrium 

 is narrow and open. The dorsal valve 

 is convex, and has a deep, narrow 

 median sinus. The length of this shell 

 is l-09 mm and the width -93 mm . This 

 form is very suggestive of the adult 



Centronella (figure 11). Figubb 11.- Trigeria 



In the older specimens the beak is lepida Hall ; young indi- 

 less prominent and in specimens more 7! idua1 ' t . e . fo ^? tlie mc ®P" 

 than 3*5 mm long the dorsal sinus becomes 

 obliterated and both valves are convex. Shells more than 



