Raymond — Common Devonian Brachiopods. 291 



to increase during these stages, the width becomes greater in 

 proportion to the length, and a number of pairs of spines are 

 added on the cardinal margin. 



Gerontic Stage. — Senile characters are not well shown except 

 in G. mucronatus. In all, this stage seems to be accompanied 

 by a thickening of the shell, a deepening of the muscle scars, 

 and a growth of the anterior part of the shell, thus repro- 

 ducing the early neanic conditions of length almost equal to 

 breadth, and an increase in the convexity of the ventral valve. 



Strophalosia truncata Hall. 



(Plate XVII, Rows 3, 4.) 

 Pal. N. Y., iv, 1867, p. 16, pi. 23, figs. 12-24. 



Nepionic Shell. — Owing to the deformation of the ventral 

 beak resulting from the method of attachment, very little can 

 be made out concerning that valve in the youngest stages 

 except that it is regularly and moderately convex. The beaks 

 of some of the dorsal valves are extremely well preserved and 

 show well the outlines of the protegulum and nepionic shell. 

 The protegulum is transversely oval, with a gently curved pos- 

 terior margin. In the best preserved specimen it is '13 mm long 

 and -155 mm wide. The dorsal valve of the nepionic shell is 

 subcircular in outline, with the hinge width about equal to the 

 greatest width below. It is convex on the umbo and often for 

 its whole length, though it is sometimes concave in front. The 

 surface is smooth, without spines (figure 8). 



Spines. — After the nepionic stage, spines are developed on 

 both valves, but more numerously on the ventral valve. On 

 the dorsal valve they are generally broken oif close to the base. 

 One specimen, however, retains two of the spines, which are 

 long, slender, and lie against the sur- 

 face of the valve. (See Plate XVII, ^^—^^ 



Row 3, No. 11.) On the ventral valve \\ZJl 



they are better preserved. They are \^^J 



most abundant along the cardinal mar- FlQrTJw8 .-strophaio8ia 

 gin and stand erect, curving in toward truncata Hall ; dorsal 

 each other from opposite sides of the beak, showing protegu- 

 beak, which suggests that they may have x ™ 6 and ne P ionic she11 - 

 been of use in anchoring the shell. 

 Over the rest of the surface the spines are directed forward. 



Anal Opening. — On the dorsal valve there is a convex chi- 

 lidium, at the apex of which is the minute anal opening. The 

 inner opening of this tube is at the anterior base of the cardi- 

 nal process, just in front of the point where it bifurcates. (See 

 Nos. 10 and 12, Row 3.) The cardinal process undergoes con- 

 siderable change during the life stages. In early neanic stages 



