556 Proceedings of Royal Society of Edinburgh. [ sess * 
radiatus , and C. condnnus. In balsam preparations the apiculi 
are hardly visible. It has been employed along with Rhizosolenice 
and Denticellce by Max Schultze in 1859 in studying the movements 
of the granules in the interior of the frustule. In Ehrenberg’s de- 
finition, the markings are given as about 6 in , 01 mm., as in some 
forms of C. radiosus, Grun. Castracane erects a var. solely on the 
presence of a striated border — a character clearly shown in Ehren- 
berg’s figure (MiJcrog., pi. xviii. fig. 39). Some specimens named 
by Van Heurck Coscuiodiscus centralis forma minor (Typ. Syn. 
Diat. Belg ., No. 531), from the Baltic, may belong rather to C. 
oculus-iridis , owing to the increase in the size of the markings out- 
wards ; C. centralis is readily distinguished from C. aster omphalus 
by the presence of the 2 unsymmetrical apiculi, and cannot be 
united with it in the same species as proposed by Grunow. The 
two processes were first observed by Mr E. Grove, F.R.M.S. 
Habitat. — Oran and Caltanisetta deposits (Ehrenberg); Glenshira 
sand (Gregory !) ; Cherbourg (H. L. Smith !) ; grey mud dredged 
in 569 fathoms, lat. 63° 40' N., long. 5° 28' E. (Ehrenberg) ; 
Richmond (Ehrenberg, Cleve and Moller !) ; some guanos (Grunow); 
South Sea, Lagos, North Sea, Baltic (Grunow) ; Heligoland 
(Schultze!);* Ascidia , Hull (Gregory!* Greville !) ; Loch Fyne 
(Gregory ! Greville !) ; Lamlash (Gregory ! Greville ! Dickie !) ; 
Firth of Forth at Granton (Rattray!) ; Melville Bay (Deby ! 
Barnett !) ; f soundings, Gulf of California (H. L. Smith !) ; 
Bally brack (O’Meara !) ; from Laminaria saccharina , Dalkey 
(O’Meara !) ; Ascidia , Dublin Bay (O’Meara !) ; Bermuda tripoli 
(Greville!); Euur deposit, Jutland (O. N. Witt!); North Atlantic, 
lat. 51° 20' N., long. 52° 25' W., 232 fathoms (O’Meara!); 
Richmond Tunnel (O’Meara !) ; Davis Straits (O’Meara !) ; Liim- 
fiord, Jutland (Hardman!); Patos Island guano (Hardman !) ;J 
Virginia (Hardman !);J Oran deposit (Deby!); Malahide 
(O’Meara!); Behring Sea, 1681 fathoms (H. L. Smith!); surface, 
Hong Kong Harbour, H.M.S. Challenger (O’Meara !) ; Monks- 
town, in tide pools (O’Meara !) ; Ascidia , Belfast (O’Meara !) ; 
Thames, at Sheerness (Grove !) ; Spezzia (Kinker !) ; Los Angelos 
* In the collection of Dr Greville. 
t In the collection of Dr Griffin. 
+ In the collection of Julien Deby. 
