Endocysts in the Genus Thalassiosira. By Thomas Comber. 491 
Dr. Cleve has, I believe, observed endocysts in a new species of 
Thalassiosira from Baffin’s Bay, which he is about shortly to figure 
and describe. In that case the endocyst closely resembles Coscino- 
discus subglobosus, a well-known Arctic form. 
From Mr. Grove I have received specimens of the original species, 
T. Nordenskioldii, in which endocysts are occasionally present within 
the frustules. Their s.v. approaches somewhat closely to that of the 
well-known Coscinodiscus excentricus . 
Description of Species. 
Thalassiosira antarctica. — Filament composed of 3-20 frustules. 
Diameter of valve 0*016-056 mm. ; surface slightly convex. Puncta 
rounded, of equal size, 20 in 0*01 mm., arranged in radiating, fre- 
quently bifurcate rows, about 18 in 0*01 mm. Centre frequently 
with one or two large granules, or short spines. Marginal apiculi 
small, inconspicuous, numerous, about 8 in 0*01 mm., sometimes 
arranged in two rows. Endocyst lenticular. Areoles irregularly 
hexagonal, 7 in 0*01 mm., decreasing in size near centre and towards 
margin, arranged in radiating rows. Inter-areolar apiculi numerous, 
either singly or in groups of two or three. Marginal spines con- 
spicuous, about 3 in 0*01 mm. 
South Shetland Islands, Antarctic Ocean. 
The ordinary valves resemble those of the Arctic species Coscino- 
discus hyalinus Grun. and C. bioculatus Grun., although these are 
described as having fasciculate markings. 
2 m 2 
