182 86 



side, with which il forms a roundly-acute angle. The ventral margin descends towards 

 the posterior end, at which point it is most convex. The upper margin slopes in a 

 rather straight line down towards the somewhat pointed, drawn-out posterior end. 

 The umbones terminate in a smooth, glossy, rounded, nodular apex, upon which the 

 small, round embryonic shell is found. Below this and radiating from the umbo, 

 an exceedingly close-set, fine, raised network extends over the whole surface to- 

 wards the outer sides. The threads of the network divide often, especially to- 

 wards the anterior and posterior ends, and are separated from each other only by 

 very fine grooves. The concentric lines of growth are coarse, irregular and fairly 

 prominent. The interior of the shell is dully white, and glossy only towards the 

 outer margins; the left valve has two cardinal teeth, of which the hinder is the 

 larger, and is triangular and tapering, separated from the upper margin of the shell 

 by a deep groove; the other tooth is pointed near its commencement and forms 

 a rather long, laminar ridge parallel with the upper margin. Between the diver- 

 gent cardinals under the umbones is a triangular space which receives the internal 

 ligament. 



Long. 9 mm., alt. 65 mm., crass. 4 mm. 



North of Koh Kut, 10 fathoms, mud ('/»). 



Unfortunately only a single left valve was obtained of this beautiful species, 

 the ray-like surface-sculpture of which is especially characteristic. 



Montacuta (Tellimya) japonica, A. Ad. 



Tclliinijn japunica, A. Adams, Ann. and Mag. Nat. Hi.st., lcSö2, p. 225. 



— Japonica, — Du.nkeh, Index moll. mar. Japon., 1882, p. 219. 



The sound of Koh Chang, 3—5 fathoms, soft clay ('"/i). W. of Koh Chang, 

 20 fathoms, mud ('/a). Koh Kahdat, 4—5 fathoms, sand and stones (*/-■). 



Long. 1'75— 5-75 mm. (long. 5-75 mm., all. 35 mm., crass. 25 mm.). 



Distribution:— Japan. 



The specimens from the Gulf of Siam correspond closely to Adam's diagnosis 

 (unfortunately he does not give a figure of his species), but when he says that: 

 "This species is more transversely oblong than T. bidenlata from the seas of Europe, 

 and the anterior side is much shorter," then only the first part of the above pas- 

 sage agrees with my observations, but with regard to the anterior end, it is almost 

 of the same length as in M. bidentata. The form of my specimens of Montacuta 

 japonica agrees therefore, in its main features, most closely with that of M. ferru- 

 ginosa, Montagu ; but like all other Montaciita-species, M. japonica probably varies 

 somewhat both in form and outline. 



Montacuta (Tellimya) paula, A. Ad. 



Ptjlhina paula, A. Adams, Proc. Zool. Soc. London, XXIV, 185(), p. 47, No. 3. 



Monlaciila paula, — Edo. Smith, Ucp. on the Lamellibrancliiata of the Challenger Exped., p. 20;^. 



Pijlhiua - — — Annals and Mag. Nat. Hist., G Ser., VIII, 1891, p. 230. 



Pijlhina pecuUaiis, — I'roc. Zool. Soc. London, XXIV. 18.")6, p. 47, No. 4. 



