LAMELLIBRANCHIATA. Ill 



lated on the lower part of the umbo, and a third set of smaller rays coming 

 in toward the margin. The first and second series only are shown in young 

 shells. In the right valve the radii are more subdued. The rays extend 

 over the cardinal expansions of both valves in neaidy uniform size. Concen- 

 tric, elevated, regularly rounded striiB of growth cross, the rays, and cancel- 

 late the surf\ice, and at intervals are crowded together, giving it a lamellose 

 aspect. 



Interior unknown. 



Ligamental area marked by one or two parallel grooves. 



A large specimen has a length of 65 mm., height 47 mm., hinge-line 55 

 mm. A specimen of medium size has a length of 51 mm., height 35 mm., 

 hinge-line 41 mm. A smaller example has a length of 18 mm., height 11 

 mm., hinge-line 13 mm. 



This species is similar in form to A. decussata, but differs in the convexity of 

 the valves and the less strongly decussated character of the ornamentation, the 

 rays being continuous and annulated by the concentric striae, while in that species 

 the rays are interrupted by strong concentric lamellae, between which are the 

 finer lines of growth. 



This species is also less aljundant and more restricted in geographical range. 



Formation and localities. In the shales of the Hamilton group on the shores of 

 Canandaigua lake, and near Bellona, Yates county, N. Y. 



ACTINOPTERIA DECUSSATA. 

 PLATE XVII, FIGS. 24, 28 ; PLATE XVIII, FIGS. 1-15 ; PLATE XX, FIG. 19 ; AND PL.A.TE LXXXIV, FIG. 4. 



Ai'ienla deciixsnta. H.\ll. Geol. Surv. N. Y. : Rep. Fourth Dist., p. 203. 1843. 

 Phronites decaumta. Hall. S. A. Miller, Cat. Am. Pal. Foss., p 202. 1877. 



Actliioptti-ia decussata. Hall. Piil. N. Y., vol. v, pt. 1. Pla!e.s and Explanations: PI. 17, fig-.-^. 24, 28; pi. 



18. fig-s. 1-1.'). Jan.. 1883. 



Shell large, sub-rhomboidal ; body sub-ovate, very oblique ; length al)out one- 

 fourth greater than the height; margins regularly curving; the anterior 

 margin sometimes nearly vertical ; posterior margin more abruptly rounded. 



