402 MR. G. S. BRADY'S MONOGRAPH OF 



furrow are strongly developed (figs. 23, 24). The surface of the shell varies much in 

 character • well-marked adult specimens are mostly marked with deep pittmgs, which 

 • (1 v roncntrieally arranged, and are deepest and closest round the margins of the valves, 

 especially on the ventral surface, where they are liable to form longitudinal furrows. 

 But ->uie varieti s exhibit only slightly impressed punctures, and in very old specimens 

 the excavations are more or less obliterated by calcareous deposit. The right valve, 

 besides being much smaller than the left, is likewise very different in shape, being pro- 

 minently beaked behind, somewhat truncate above, and deeply sinuated on the ventral 



The terminal claws of the lower antennae' are very short, slender ; and there 

 mature of three setse on the middle of the inner margin, similar to that of the 

 following species, but without the pectination of the long filament. The urticating seta 

 is very short in the female (see Plate XXXIX. fig. 4). 

 Length -gV in., height fa in. 



marinn. 



Ihib. In deep water and occasionally between tide-marks. 



(Mi 



Minch (Mr. J. G. Jeffreys) ; Isle of Skye, Lamlash Bay, Channel Islands, Falmouth, Burrow 



M. Nor 



Lerwick, Cumbrae, and Oban {Mr. D. Robertson), off Devonshire coast, 60 fathoms {Mr. C. S. Bate) j 

 in -lull-sand from South Wales and Stranraer, Aran, and Roundstone, and dredged in Birterbuy 



TV. C. Williamson 



d) 



/3 



10. Cytherb albomactjlata, Baird. (Plate XXVIII. figs. 33-39, and Plate XXXIX 



fig. 3.) 



Cythere albomaculata, Baird, Brit. Entom. p. 169, tab. xx. fig. 7. 

 ■ alba (young), Baird, loc.cit. p. 170, tab. xx. fig. 6. 



British type. Distribution: Recent — Great Britain, Ireland, Norway, Bay of Biscay, Levant, Cape 

 Verd. Fossil — Glacial clays and raised beaches, Scotland, Ireland, Norway. 



Valves, as seen from the side, oblong, subreniform, nearly equal in diameter through- 

 out ; height equal to rather more than half the length. Anterior margin well rounded ; 

 posterior obliquely rounded, and somewhat angular at its junction with the ventral 

 border. Dorsal margin forming a flattened arch; ventral margin deeply incurved 

 it its anterior third, and curving upwards behind. Outline, as seen from, above com- 

 pressed, oblong, widest in the middle, and gradually tapering to the extremities, which 

 are pointed, width equal to more than one-third of the length. End view oval, rounded 

 above and keeled below. The valves are bordered in front and below by a broad, flat- 

 tened flange or belt, which is marked with thickly set, transverse, hair-like lines (fig. 38). 

 The striated keel thus formed by the junction of the two valves is very conspicuous on 

 the ventral and anterior aspects of the shell (figs. 35, 36). Surface smooth and polished, 

 clothed with short scattered hairs ; pellucid and marked with patches of black or olive- 

 green ; old specimens and those from shell-sand and deep water are mostly opaque white. 

 The hinge-joint is exceedingly well developed, the left valve bearing a strong bar which 

 is received into a groove between the terminal processes of the opposite valve (fig. 39 )• 



