REPORT ON TITE IUATnMACE.E. 1G7 



parts connected with these fragments may be explained by the long cylindrical forms of 

 the frustules. 



The following are the essential characteristics of the genus Ethmodiscus : — (1.) The 

 extremely delicate granulation or striation of the frustule ; (2.) the discoidal form and 

 notable convexity of the valves ; (3.) the great development of the connecting zone, which 

 may sometimes cause the axial line to exceed the length of the transverse diameter; (4.) 

 the presence of small points arranged in a quadrate manner on that zone; and (5.) the 

 frequent occurrence of distinct elevated granules, which rise upon the valves in a coronal 

 or radial manner. 



The following new species are included in this genus : — 



Ethmodiscus punctiger, n. sp. (Plate III. fig. 1.) 



Valvis convexissimis, finissime radiato-punctulatis, denticulorum corona marginali 

 decoratis, et ad marginem granulorum ordine signatis. Diametrum = 143 m. Prope 

 Yedo, in mari Japonico. 



This large and beautiful disc comes from a very interesting collection of pelagic 

 Diatoms made in the Bay of Yedo. It possesses a very convex form, and is ornamented 

 with delicate radiating punctated striae. It has a submarginal corona of distinct points 

 or denticules, and its border is marked by a row of very small granules. 



Ethmodiscus convexus, n. sp. (Plate III. fig. 9.) 



Valvis admodum convexis subinconspicue punctulatis ; denticulis medio raris, ad mar- 

 ginem dense ordinatis. Diametrum= 123 n. In mari Arafura. 



This beautiful species was found in the Arafura Sea. Its disc is markedly convex, 

 bears an almost invisible striation, and is ornamented with very minute denticules, while 

 near its periphery a circle of similar denticules is also found. This species cannot be eon- 

 founded with any Coscinodiscus on account of the extreme delicacy of its ornamentation 

 and the decided convexity of its valves, which is equal in extent to two-thirds of their 

 radius. The specific name has reference to the form of the valves. 



EthmodiscuS;radiatus, n. sp. (Plate XII. fig. 9.) 



Forma grandiuscula finissime striolata ; zona lata marginali inordinate granulata, a 

 qua granulorum radii plus minus ad centrum pergunt ; media superficies nonnullis granulis 

 sparsa ; distinctiorum granulorum corona marginali. In mari Arafura. 



This species is also from the Arafura Sea. It is of discoidal form and bears extremely 

 delicate strise. It exhibits, towards the margin, a large belt of small granules confusedly 

 disposed, and from this belt there run towards the centre several straight rows of granules. 



