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SCHIZASTER LIMICOLA. 77 
* Schizaster (Periaster) limicola A. Ao. 
Schizaster (Periaster) limicola Agass, Bull. M. C. Z., V., No. 9, p. 193, PL III., 1878. 
PI. XXVI. Fif/S. 5, 6. 
This species belongs to the generic group of Schizaster separated as Peri- 
aster by D'Orbigiiy from the genuine Schizaster. The test is quite globular, 
when seen from above the outline is somewhat angular, the posterior ex- 
tremity is vertically truncated, with a slight keel between the posterior 
petals near the apex ; the anterior extremity has a shallow ambulacral 
groove, and is vertically truncated from the edge of the peripetalous fasciole. 
The lateral anterior petals are nearly twice as long as the posterior one, as 
well as broader. The petals are all about equally sunken. The peripetalous 
fasciole has the shape and position of that of Schizaster proper; the anal 
fasciole is narrow, extending only a short distance on the sides of the test. 
The test is thickly covered with primary tubercles of a uniform size, car- 
rying short, slightly curved spines on the sides ; the tubercles are somewhat 
more crowded within the fasciole and on the abactinal region of the odd pos- 
terior interambulacral area. The coronal plates between the fasciole and the 
anal system are comparatively bai'e, having only few tubercles on the outer 
edges. On the actinal side the primary tubercles are larger, more distant, 
except on the actinal plastron, where they are closely crowded, and caiTy 
longer, larger, and curved primary spines. The actinal lip is very sharp and 
prominent ; the actinal membrane carries one large exterior row of plates 
round the anterior edge of the actinostome, and smaller irregular plates over 
the rest of the actinal surface. The anal system is comparatively small for 
so large a species. The separation of this group of Schizaster as a generic 
type seems very doubtful. It is based solely upon the more globular outline 
of the test, and the discontinuity of the latero-anal fasciole. It may be con- 
venient to form a snbgeneric group with these characters ; but when we 
attempt to draw the line between such forms as S. ventricosus and S.japonicus, 
it becomes most difficult, if not impossible, to draw the line of demarkation 
between the generic and subgeneric types. 
We find the same difficulty in attempting to define the numerous generic 
subdivisions indicated by Troschel for the genus Tripylus and its allied forms, 
which pass insensibly to Faorina and the like, while in Schizaster the devia- 
tions are in the direction of modifications passing into Periaster, Epiaster, 
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