ROTALIIDAE 125 



Cushman has separated our form apparently on account of the absence of the 

 secondary apertures described by Rhumbler. His varietal name is not very happy, as 

 we have found these irregular forms not only in British waters, but wherever D. 

 globidaris is plentiful. 



296. Discorbis mediterranensis (d'Orbigny) (F 332). 

 Five stations: 27, 145 ; WS 25, 33 ; MS 68. 



Very common at WS 25, frequent to rare at the other stations. 



297. Discorbis vilardeboanus (d'Orbigny) (F 333). 

 Four stations: 144, 149; WS 33 ; MS 68. 



Common at St. 149 and MS 68 and very variable in height at the latter station. 

 Rarer at St. 144, where the most typical specimens were found, and very rare at WS 33. 



298. Discorbis rosaceus (d'Orbigny) (F 334). 



Eleven stations: 123, 131 ; WS 25, 31, 33, 40, 42, 51, 66, 351; MS 68. 



Small specimens and rare everjrwhere, except at Sts. WS 25, 33 and 66. At the first 

 of these it is very common. 



299. Discorbis chasteri (Heron-Allen and Earland) (F 352). 

 Two stations: 140; WS 33. 



A single large individual at St. 140, many large and small at WS 33. 



300. Discorbis margaritaceus, sp.n. (Plate IV, figs. 23-25). 

 One station: WS 25. 



Test free, circular in outline, dorsal side convex, peripheral edge rounded, ventral 

 side rounded and sinking into a deep umbilicus ; consisting of about two convolutions, 

 six chambers in the final convolution ; sutures on dorsal side oblique, flush but strongly 

 marked; sutures on ventral side obscure and flush; dorsal surface granular, ventral 

 surface covered with very minute beads arranged in radial lines across the chambers 

 into the umbilical recess. Aperture a minute slit on inner edge of final chamber. The 

 general aspect of the shell is lustrous or pearly, owing to the difi'raction eff'ects produced 

 by the granulation of the dorsal surface, and the beads on the ventral surface which is the 

 brighter of the two. 



Diameter up to 0-3 mm., height about 0-05 mm. 



A few specimens only of this pretty shell, which is probably allied to D. parisiensis 

 (d'Orbigny), were found. 



301. Discorbis subobtusus, Cushman. 



Discorbis subobfusa, Cushman, 1921, FP, p. 304, pi. Ixx, fig. 2. 

 One station: WS 351. 



Three specimens found at this station at a depth of 1170 m. agree fairly well with 

 Cushman's figure except in size. They are much smaller, the largest being only 0-35 mm. 



13-2 



