77 173 
Epc. Smiru'! says regarding this species that “The radiating coste 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 cost, 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 striz. 
Lucina (Phacoides) pulchella, n. sp. 
(Pl. III, Figs. 13-15). 
This little species is irregularly rounded, rather thin, white, convex, inequi- 
lateral. The sculpture consists of about 11 stout, strong, radiating coste, 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 lire. 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 lire 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 (?/2). Koh Kram, 30 fathoms (1/2). Koh Chuen (?/2). 
E. of Cape Liant, 9 fathoms, shells (‘/2). Koh Mesan, 15 fathoms, stones (*/2). Between 
Koh Mesan and Cape Liant, 9 fathoms, sand (6). S. of Koh Samit, 20 fathoms, 
mud (t/2). S. of Koh Chuen, soft clay and mud (*/z). Between Koh Chuen and 
Koh Chang, 15 fathoms, mud (‘/2). Koh Kahdat, 1—5 fathoms, sand and stones (3). 
Between Koh Kahdat and Koh Kut, 6 fathoms, clay mixed with sand (°/2).  W. of 
Koh Kut, 15 fathoms (2). W. of Koh Kut, 30 fathoms, sand and mud (*/2). 
This little species is most nearly related to the small group of species: — 
seminula, Gould, pisum, Reeve, and Semperiana, Issel, from which it differs, however, 
1 Report on the Lamellibranchiata of the Challenger Expedition, p. 181. 
* See REEveE’s figure, pl. XI, fig. 66 b. 
8 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 Epc. Smiru states) “very minutely crenulated,” 
