77 17;5 



Edg. Smith ' says regarding this species lliat "The radiating costæ in this 

 species are only about eleven in number, very strong, and crossed by about sixteen 

 stout concentric ridges, which are somewhat nodose upon the costæ, and gradually 

 attenuated at both ends, which are devoid of longitudinal ribs." This does not 

 exactly correspond with the rather large quantity of material which I have at my 

 disposal from the Gulf of Siam. From this it appears that the radiating ribs are 

 not so prominent at the anterior end - as at the middle, where there are about 

 15—20 radiating ribs and (in a specimen measuring 6 mm. in height) about 23 

 concentric folds; ' the latter are, at the posterior end, almost smooth and without 

 radiating striæ. 



Lucina (Phacoides) pulchella, n. sp. 



(PI. Ill, Figs. 13-15). 



This little species is irregularly rounded, rather thin, white, convex, inequi- 

 lateral. The sculpture consists of about 11 stout, strong, radiating costæ, of which 

 several divide, so that in larger specimens there are about 20 ribs at the ventral 

 side. The ribs, which are broader than the interstices between them, are crossed 

 by close-set, fine, raised concentric liræ. The radiating ribs are considerably pre- 

 dominant over the concentric lines. At the anterior and posterior ends of the 

 valves the radiating ribs are absent, but the thread-like concentric liræ are present. 

 The lunule, which is smooth and oblong-cordate, is deeply excavated beneath the 

 overcurving umbones, each of which is smooth at the bluntish tip. The area is 

 oblong, rather narrow, and smooth. In the left valve are two cardinal teeth, and 

 in the right valve there is one. The lateral teeth are small in both the valves. 

 The somewhat thickened inner margin is dentate, most decidedly towards the ven- 

 tral and front sides; at the upper part of the anterior end these marginal teeth are 

 very fine and small, and they disappear at the upper part of the posterior end. 



Long. 4 mm., alt. 4 mm., crass. 3 mm. 



Koh Lan, 30 fathoms, mud (-/a). Koli Kram, 30 fathoms ('/a). Koh Chuen (^/s). 

 E. of Cape Liant, 9 fathoms, shells ('/a). Koh Mesan, 15 fathoms, stones (-Vs). Between 

 Koh Mesan and Cape Liant, 9 fathoms, sand (6). S. of Koh Samit, 20 fathoms, 

 mud ('is). S. of Koh Chuen, soft clay and mud ('Vs). Between Koh Chuen and 

 Koh Chang, 15 fathoms, mud (Va). Koh Kahdat, 1—5 fathoms, sand and stones (3). 

 Between Koh Kahdat and Koh Kut, 6 fathoms, clay mixed with sand (''/a). W. of 

 Koh Kut, 15 fathoms (2). W. of Koh Kut, 30 fathoms, sand and mud {*h). 



This. little species is most nearly related to the small group of species: — 

 scminnla, Gould, pisum, Reeve, and Semperiana, Issel, from which it differs, however, 



' Report on the Lamellibranchiata of the Challenger Expedition, p. 181. 



'' See Rkevi;"s figure, pi. XI, fig. (16 b. 



' This causes the folds to become strongly crenulated, which results in the lower margin of the 

 valves becoming strongly dentate within; the lower inner posterior side, owing to the very feeble radial 

 striation, is only (as Edg. Smith states) "very minutely crenulated." 



