110 PALAEONTOLOGY OF NEW YORK. 



Interior unknown. 



Ligamental area with one or two lonjritudinal grooves. 



Tlic s]iccimcn lias a hMiQth of IS mm.. liciL'ht IH mm. 



Formation and locality. In the Marcelhis shale at East Bloomfield, Ontario 

 countv, N. Y. 



ACTINOPTERIA SUBDECUSSATA. 

 I't.ATK XVII, KIGS. 23, iV-aT. 29-.'!l ; and PLATE XIX. KIG. IV 



Plertmites siMtciuisala, II.vll. MS., vol. v. 1877. 



" . •• S. A. Miller in Cat. Am. Pal. Fo.s.«., p. 202. 1877. 



AitlnophrUi .Kuhdtcnj<.ini(i. Ilvi.i.. Pal. N. Y., vol. v, pt. 1. Plates and Kxplaiiations : PI. 17, tig-s. 23, 25- 



27. 2!l-31 ; 1)1. 111. tij,'. 2.'). .Jan., 1S83. 



Shell hirge, siili-ilinmboidal, ver\' oblique; body elongate sub-ovate ; height 

 al)uut oiic-tliinl less than tlic Icuutli ; margins regularly curved, becoming 

 more extended on the posterior side. 



The left valve, in old specimens, has the umbo convex above, depressed- 

 convex or flat below, while in young specimens the umbo is altogether con- 

 vex or gibbous. Might valve moderately convex near the umbo, tiat or 

 concave below the middle. 



Hinge-line straight, length about one-fifth less than the length of the shell, 

 not extending as far as the posterior margin of the left valve, hut extending 

 beyond the posterior margin of the right ^ alve. 



Beak acute, directed forward, somewhat prominent, anterior nearly 

 terminal. Umbonal region (in young shells) well marked by the sulci ; 

 umbonal angle acute. 



Ear very small, separated by a vertical sulcus. Wing large, triangular, 

 defined in young shells by the abrupt convexity of the post-cardinal slope ; 

 in old specimens not distinctly defined ; margin concave ; extremity acute. 

 The wing of the right valve is larger, and extends beyond the margin of the 

 shell. 



Test comparatively thin, marked with regular, sub-angular, alternating radii, 

 the stronger ones extending from the summit of the umbo; a second set interca- 



