144 THE VOYAGE OF H.M.S. CHALLENGER 



Actinocyclus pruinosus, n. sp. (Plate IV. fig. 2.) 



Valvis ad marginem dense deinde rarius punctulatis ; centrum area hyalina nonnulis 

 punctulis medio signata, a qua pluriinse punctulorum lineae circum distribuuntur. 

 Diametrum 100 m. In mari Pacifico. 



This very elegant form does not entirely satisfy the generic definition given by 

 Ehrenberg. Thus, although a beautiful round hyaline pseudo-nodule occurs near the 

 circumference, the disc, which is divided into thirty-five distinct segments by salient 

 punctated radii, is but sparsely granulated, while, with the exception of a single fasciculus, 

 the granules are densely disposed near the circumference and around the centre, but 

 become more rare over a moderately wide subcentral or submedian area. The 

 centre consists of an irregular smooth area, in the middle of which a small group 

 of points occurs. The diameter of the valve, which was collected in the Pacific Ocean, 

 is 100 ft. 



Actinocyclus fasciculatus, n. sp. (Plate IV. fig. 8.) 



Valvis cellulosis per lineas cellularum radiantes divisis ; segmenta cellulis fasciculatim 

 dispositis, ad marginem in punctis decussatim distributis transeuntibus, areola umbilicali 

 tribus cellulis medio signatis ; pseudonodulum submarginale evidens. Fossilis ad Eich- 

 mond in Virginia. 



The cellulated surface of this form is divided into segments by numerous radiating 

 moniliform lines of equal size and originating from a small central area, the middle of 

 which is occupied by three small cellules. The segments are ornamented by fasciculately 

 disposed cellules of uniform size except in an outer zone, where the margin is provided 

 with very minute granules arranged in a decussate manner. The submarginal pseudo- 

 nodule is well seen. The frustule was found in a fossilised condition at Richmond, 

 Virginia. 



The specific name has reference to the fasciculate appearance of the sculpturing of the 

 component segments of the valve. 



From the consideration of this and the foregoing species it is manifest that the 

 discoidal granulated form of the valve, combined with the presence of an intramarginal 

 pseudo-nodule, can alone be regarded as absolutely distinctive of the present genus, the 

 character of the granulation varying considerably between divergent extremes. 



Actinocyclus fasciculatus, n. sp., var. nov. (Plate IV. fig. 8 bis.) 



A frustule very similar to that last described is here shown. It differs, however, in 

 it3 smaller size, and in its locality, having been collected in the Atlantic at lat. 37° 24' N. 

 and long. 25° 13' W. 



