318 DESCEIPTION OF [Polygastrica. 



AnrnoRA Lyhica. — Dorsum convex its entire length ; venter con- 

 cave; sides punctate; striate on their inner margin. (1-2 8 8th.) Found 

 in the Oasis of Siva, Mexico, XJnited States, &c. (P. 15, f. 38.) 



A. rimosa. — Discovered and named by Ehrenberg, among other 

 American Bacillwria. 



A. Fischeri. — Turgid at the middle, ends widely truncate ; thi'ee 

 longitudinal marginal lines ; central lines obsolete. (1-5 76th.) Carls- 

 bad. Probably a variety only of A. Coffeaformis. 



A. Amj^hioxys (Bailey.) — Ventral side rectangular, with slightly 

 rounded ends, and two arcuate bands of stria?, which are broadest 

 near the centre ; back convex, minutely striate ; sides convex above, 

 minutely sti'iate ; concave below, strongly striate ; ends produced and 

 rostellate. The side view of this species bears a striking resemblance 

 to Eunotia amphioxxjs (Ehr.) 



Genus An ATJXirs. — Lorica simple, bivalve, compressed, subquadrate; 

 spontaneous fission complete, hence no concatenation. This genus 

 approaches BiddulpMa by the constrictions on its sides, but is without 

 tubular processes, and lateral aperiures. 



A. scalaris. — Smooth, turgid in the young state ; but when full 

 grown, very wide and much flattened, with foui', six, eight, fourteen 

 lateral constrictions, which give it, when viewed on the side, a 

 ladder-like (sealarifoiTti) appearance. Diameter 1 -480th to 1-1 80th. 

 Antarctic Ocean, 



A. campy locUsmcs. — Quadi'angular ; each valve very much com- 

 pressed, triangular, with obtuse angles ; with two slight constrictions 

 laterally. It has the habit of an unequal-sided Triceratium, or of a 

 Campylodisctis. Diameter 1-3 72nd. Bermuda. 



Genus Aeachnoidiscus (Dcane.) — Lorica circultu", discoid, bivalve, 

 divided into cells (locuK) by incomplete septa ; centre of disc clear, 

 occupied by a foramen, surrounded by denticles, equal in number to 

 the rays, and ^\'ith an external contiguous circle of puncta (foramina.) 

 Interspaces between the rays occupied by fine concentric or trans- 

 verse lines ; also, at the periphery, by short projecting septa. 



The disc, in its markings, has been compared to a spider's web — 

 hence the name. Its affinity is with Autinopfychus. Mr. Shadbolt 

 has ijitijnatoly examined the structuie of the shell. He says — "It 



