173 



Measurements of the Holotype : — Length 3.5 mm., height 2 mm., diameter 1.2 mm. 

 Habitat : — The unique Holotype of M. sibogai was dredged at the Anchorage off 

 Lirung, Salibabu Island (St. 133). 



Genus Isoconcha Gen. nov. 



191 1. Isoconcha sibogai Dautzenberg & Fischer, H., in Pelseneer "Siboga" Lamellibranches 

 (Anat.), p. 47, pi. XVI, fig. 12, pi. XVII, fig. i. 



In his account of the Montacutidae Pelseneer included at the instance of Messieurs 

 P. Dautzenberg and H. Fischer two new generic names — Isoconcha and Bilobaria^ and 

 described their soft parts. The shells of neither of the two gênera hâve been described so far, 

 and unfortunately the box with label Bilobaria in the collection received froni Paris, was found 

 to be empty; this generic name must, therefore, remain a nomen inquirendum. Oi Isoconcha 

 a shell is available, and I agrée with Messieurs Dautzenberg and Fischer that it represents an 

 undescribed genus. 



The following is a description of the shell of Isoconcha : — Shell small, subtrapezoidal, 

 moderately solid, subequilateral, inflated, medially compressed ; thin deciduous epiderms covering 

 non-nacreous shell ; umbones subcentral, moderately tumid ; sculpture consisting of concentric 

 striae ; no latéral teeth, a single cardinal tooth arising from margin of shell centrally below 

 umbones and a corresponding socket in each valve; ligament long, thin, external ; no resilium; 

 palliai line entire. Génotype: — Isoconcha sibogai sp. nov. The soft parts of the génotype hâve 

 been described by Pelseneer. 



I am also of opinion that Hedley's species ^) Turquetia intégra dredged from east of 

 Sydney is also congeneric with /. sibogai^ and should be referred to Isoconcha. 



I. Isocojicha sibogai sp. nov. (Plate IX, figs. 9 — 12). 



/. sibogai is closely allied to /. intégra (Hedley), but is distinguished by the shell being 

 less convex and distinctly compressed in the middle, the subtruncated anterior end, the ventral 

 margin more arched, the umbones less prominent, the sculpture consisting of concentric striae, 

 and the hinge teeth less strongly developed. 



Measurements of Holotype: — Length 7 mm., height 4mm., diameter 2.6mm. 



Habitat : — The unique Holotype was brought up in a deep-sea trawl at St. 300 

 (io°48'.6S., i23°23^iE., 918 mètres). 



Family Geloiniidae. 



Genus Geloina Gray. 



181 8. Cyrena (ex parte) Lamarck, Anim. sans Vertèb., V, p. 5 5 1 bis. 



1847. Geloina Gray, Proc. Zool. Soc. London, p. 184. 



i86r. Geloina Môrch, Journ. ConchylioL, IX, p. 348. 



1897. Cyrena von Martens, Weber's Zool.Ergebn. Reise Ost. Ind., IV, Sûss.-Brackw.iI/<7///^i-rrt, p.90. 



1903. Cyrena Dali, Trans. Wagner Free Inst. Philadelphia, III, p. 1441. 



i) Hedley, C. — Mem. Austral. Mus., VI, p. 364, pi. LXVI, figs. 7 — 10 (1907). 



