46 
Wallich^ on Siliceous Organisms. 
both in Asteromphalus Bud in Asterolampra, are formed upon 
the same general plan. They consist of an expanded base, 
by the margins of which they are united together, or to the 
basal ray ; and of the free hyaline arm which is directed 
towards the circumference of the valve. The curvature oc- 
casionally seen in the last-named portion of the rays is 
extremely variable in extent. The connecting sutures, on 
the other hand, afford a tolerably constant character, and are 
important, inasmuch as on the shape of the connected por- 
tions of the rays depends their contour. The basal rays also 
yield good characters, their capitate extremities being either 
wholly or partially overlapped by the true rays, and being 
either angular, clavate, emarginate, or simply elongated. 
ASTEROMPHALUS, EJir, 
Frustules free ; disciform. Valves orbicular, sub- orbicular, 
or oblong, with an indefinite number of hyaline rays ar- 
ranged round the capitate extremity, or one or more basal 
rays. Front view of frustule exhibiting imperfect septa. 
Cellulation of inter-radial spaces hexagonal. 
Section I. — Basal ray single. 
A. imbricatus, n. sp. — Rays numerous, arranged more or 
less excentrically round the clavate elongated extremity of 
the basal ray ; one ray opposite to and continuous with the 
basal ray. Sutures angular. 
Var. ^, Sutures plane. 
Var. y. Capitate extremity of basal ray emarginate. 
This remarkably beautiful disc presents us with one 
extreme of the series, of which A. sarcophagus, a species 
immediately to be noticed, constitutes the other. The basal 
ray being directed towards the observer, the true rays on 
either side, gradually diminish in size till they reach the odd 
ray, which is only about half the size of the largest one. 
The arrangement is thus rendered very excentrical. Ex- 
tremity of basal ray much produced. Cellulation conspicuous. 
Diameter of valve -0029. Fig. 9. 
From Salpse, Bay of Bengal. April, 1857. 
A, elegans, Grev. — This form represents a variety of Dr. 
also been noticed, in a few species, by other observers since Mr. Sliadbolt's 
discovery. It vrill be found, however, I believe, in most discoid forms, 
although only observable in those that have conspicuous markings and 
liyaline valves. It certainly occurs in Uupodisaus, Asterolampra, Campy- 
lodiscus, and in the sigmoidally bent form of Biddulphia turgida. In the, 
last two, the valves are placed at right angles to each other. ; 
