314 DESCRIPTION OF {Poli/gastrica, 



Genus AcTiNOPTTCirtJs, (Ehr.) — Lorica bivalve, in the form of a 

 circular disc, with coincident external rays and internal septa. Surface 

 cellular. Individuals solitary. This genus differs from Gallmiellaj 

 by its individuals being distinct, not concatenated ; from Actinocrjclus, 

 by its lorica having both rays and septa ; for Aetinocyclus is destitute 

 of internal partitions. 



Tliis genus, instituted by Ehrenberg since Actinocyclus, must 

 embrace many species formerly numbered with the latter, — indeed, 

 all those with internal septa; and there is no doubt, that those 

 having like specific names in the two allied genera, are really 

 identical. 



A. terna/rius. — Disc with three septa. Fossil in chalk marl. 



A. qmnarius. — Disc with five septa. Fossil. Richmond, Virginia. 



A. hexcopterus. — Conical, rays or internal septa six, solid ; border 

 of disc thick, sinuose, dentate internally. Can it be a calcareous 

 ■pavHcle of anjEchinoderm, ComopeUa? Vera Cruz. Fossil (P. 14, f. 31.) 



A. nonarius. — Similar, with nine rays or septa. Peru and North 

 America. 



A. denarius, with ten radiating septa. Richmond, U.S. 



A. vicenarius, with twenty radiating septa. 



A. Jupiter, with twenty -four radiating septa. Richmond, Virginia, 

 (P. 14, f. 28.) 



Other forms are met with having seven, eight, twelve, and seven- 

 teen septa, and might, on the same principles as the foregoing, be 

 considered distinct species. 



A. qtiaternarius, has four radiating partitions, and consequently 

 the same number of intermediate cells. Diameter 1 -552nd. Fossil 

 in chalk marl. 



A. velatiis, has six rays, and a loosely cellular disc; its surface 

 appearing as if veiled by a delicately spotted membrane. Diameter 

 1-3 72nd. 



A. biternarius, is allied to the preceding species, and has the same 

 number of septa ; but its surface is adorned with obliquely 

 dotted lines. 



A. senarius. — Diff'ers from A. bifernarius only in the sculpturing 

 of its sui-face ; fossil, .^gina. 



