320 DESCRIPTION OF l^Polygastrica. 



between the septa, umbilicus produced to margin by radii, which are 

 smooth and flat — the one preceding between the two united septa, 

 smaller than the other. Spaces between radii elegantly marked by 

 dots, aiTangcd in eccentric cui'ves. It diiFers from Asterolampra, 

 where all the divisions are symmetrical ; from Asteromphalus, the two 

 umbilical septa are nearly parallel, and the corresponding marginal 

 radius is wanting. Three si^ecics were found by A. S. Johnson, Esq., 

 in Piscataway and E,ichmond, (N. A.) earths; fossil guano from the 

 Chiacha Islands off the coast of Peru ; and in the Bermuda earth, 

 along with specimens of Asterolampra 8eptenaria, and JSupodiscus ? 

 Tripes, (Silliman's American Journal, 1852.) 



A. qidnarim. — Five marginal radii and umbilical divisions. 



A. senarius, with six radii and divisions. 



A. nonarius, with nine radii and dii-isions. 



Genus Asteholampea, (Ehi'.) — This genus is intermediate between 

 Actinocyclus and Actinoptychus. Lorica simple, symmetrical, bivalve, 

 and circular; divided by imperfect internal partitions (dissepiments,) 

 alternating with the perfect radii visible on the surface. Form very 

 elegant ; but fission being complete, it does not occur in chains. 



A. Maryland ica. — Pays eight, reaching the margin ; and as many 

 alternating partitions, radiating also from the centre, but incomiilcte, 

 Curved rows of puncta occupy the interspaces. Diameter l-192ud. 

 (P. 14, f. 33.) 



Genus AsTEE.OMPHALTJS,(Ehr.) — Lorica simple, symmetrical, bivalve, 

 and orbicular. Fission complete ; hence individuals not found in 

 chains. Each disc marked by alternating rays, giving the appearance 

 of a double star. Umbilical rays (imperfect partitions, septa) not 

 attaining the margin, two parallel, the rest divergent. Marginal 

 rays smooth, plane, and one of them, in aU species and individuals, 

 wanting, or so obsolete, that two umbilical, one on either side of it, 

 become parallel, 



The fossil American genus Asterolampra, approaches nearest to 

 Asteromphalus, but differs from this by all its rays being perfect, and 

 by their alternation and divergence being also perfect and symme- 

 trical. 



A. Darwinii. — Umbilical rays, five ; flexuose, with four marginal 

 rays, the fifth obsolete. Diameter 1 -960th. Antarctic Ocean. 



