85 LSI 



Montacuta costata n. sp. 



(PI. Ill, Fig. 27). 



Tills little species is obloiig-ovate and rather flat, white, semitransparent, some- 

 what glossy and provided with a thin yellowish epidermis. The anterior end is 

 regularly rounded, the posterior end forms a somewhat sharp angle with the dorsal 

 side, and then slopes in a straight line down towards the ventral side, with which 

 it forms a roundly-acute angle; a sharp keel extends from the latter across the 

 shell up towards the apex. The ventral margin is rather straight. The umbones 

 which are not very prominent, are situated towards the posterior end. The sur- 

 face is smooth around the apex, but gradually slight, concentric costæ are seen to 

 appear, which upon the rest of the shell (about 1 mm. from tlie top right down 

 to the ventral margin) occur as numerous, close-set, parallel, uniform, rounded 

 ridges; at the keel mentioned above they turn abruptly and ascend parallel to each 

 other straight up towards the sloping posterior side of the upper margin. The 

 interior of the valves is white and glossy. The left valve has two erect lamellar 

 very divergent long teeth, of which the posterior is rather more strongly developed; 

 they are separated by a broad triangular space, and stand out freely from the outer 

 margin. The shell-margin is somewhat thickened, especially along the ventral side. 



Long. 3 mm., alt. 17 mm., crass. 1 mm. 



West of Koh Kut, 30 fathoms, sand and mud (V2). 



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

 it is perhaps not full-grown; when complete specimens are at hand, it will be 

 proved whether 1 am right in referring it to the genus Montacuta. With regard to 

 the generic name Montacuta, it was given in 1819 to this group of the Lamelli- 

 branchiata by Turton, under the form of Montacuta (after the zoologist George 

 Montagu). In 1828 Fleming employed the generic name Montagua for a group of 

 Aeolidae, but Rud. Bergh afterwards (1864j replaced this by the name Cratena; in 

 1825 Desmarest employed the name Montagua for a crustacean, but this was after- 

 wards obliged to give place to Callianassa, Leach. In 1852 Leach proposed the 

 name Montagua for a group of Trochus-foims (= Jujubinus, Monterosato). Bronn, 

 and later Hucquoy, Dautzenberg and Dollfus, and also Lamy, use the name 

 Montaguia for this group of Lamellibranchiata,' but according io the rules for 

 zoological nomenclature now in force this is not admissible, it should be Montagua, 

 if it could be used at all. 



Montacuta venusta n. sp, 



(PI. Ill, Figs. 28-29). 



This species is oblong-ovate, donaciform, rather flat and white. The umbones 

 are situated towards the front end, in the anterior third of the shell. The anterior 

 end slopes in a slight curve abruptly down from the apex towards the ventral 



' P. FiscHEH says also (Manuel de Conchyliologie, p. 1027) that Montaguia is tlie most correct 

 foi in of the name. 



