allied to Arcoperna ^) Conrad, and may eventually hâve to be combined with it. The form, 

 which I describe under the name 5". sidogae, could with equal justification be referred to Arcoperna. 



I. Solamen sibogae sp. nov. (Plate II, figs. 44, 45). 



The following is a description of this new species: — Species of large size, globose, very 

 inflated; shell moderately thick, transluscent ; equivalve, inaequilateral ; umbones very large, 

 prominent, obliquely inclined forwards and inwards, almost touching in the middle line-, anterior 

 margin very convexly arched, from above the middle suddenly curving inwards to pass gradually 

 into the ovately rounded ventral border; posterior margin slightly curvëd, shorter than anterior; 

 hinge-line greatly arched, very narrow, with an internai ligamental groove, sculpture consisting 

 of very regular, fine radiais separated by thread-like interspaces ; concentric sculpture consisting 

 of few growth-lines only. 



Length 25 mm.; height 18.3 mm.; diameter 19.2 mm. 



Habitat : — The unique Holotype was dredged off the North East coast of Java at St. 5 

 (7°46'S., ii4°3o'.5E., depth 330 mètres). 



S. sibogae is closely allied to Solamen rex Iredale ^) from the Twofoid Bay, Australia 

 and probably to Arcoperna recens Tate ^) from Port Espérance, Tasmania, but is distinguished 

 by its shape and very regular radial sculpture. 



Family Isognomoniidae. 



Genus Isognomon Solander. 



1758. Ostrea (ex parte), Linnaeus, Syst. Nat., (éd. X), p. 699. 

 1786. Isognomon Solander, Portland Mus. Catalogue, p. 41. 

 1788. Melina Retzius, Dissert. Hist. Nat. Test., p. 22. 



1798. Isogomun Roding, Mus. Boltenianum, p. 168. 



1799. Perna Lamarck, Mém. Soc. d'Hist. Nat. Paris, p. 82. 



18 II. Sutura Megerle, Mag. Ges. Naturf. Fr. Berlin, V (i), p. 65. 

 1817. Melina Schumacher, Essai Nouv. Syst., p. ni. 

 1847. Melina Gray, Proc. Zool. Soc. London, p. 200. 



1857. Isognomon Adams, H. & A., Gen. Rec. Moll., II, p. 526. 



1858. Pei'na Reeve, Conch. Icon., XI, Perna, pi. I (explanation). 

 1886. Perna Fischer, P., Man. Conchyliol., p. 956. 



1890. Perna Clessin in Martini Chemn. Conch. -Cab. (N. F.), VIII (I), Malleacea, p. 26. 

 1898. Melina Dali, Trans. Wagner Free Inst. Sci. Philadelphia, III, p. 665. 

 19 15. Isognomon Iredale, Proc. Malacol. Soc. London, XI, p. 303. 



1924. Pedalion Iredale, Proc. Linn. Soc. N. S. Wales, XLIX, p. 190. 



1925. Pedalion (Sect. Isogonum) Oostingh, Geol. Comm. Agr. Univ. Wageningen, N*^ 9, p. 244. 



As Iredale pointed out (19 15) Isognomon Solander must replace Melina Retzius, but 

 there seems no justification for his later suggestion that Pedalion (Solander) Huddersford should 

 replace Isognomon. 



i) Conrad, T. A. — Amer. Journ. Conch. I, p. 140 (1865): See also Tate, R., Proc. Malacol. Soc. London, II, p. 181 (1897). 



2) Iredale, T. — Proc. Linn. Soc. N. S. Wales, XLIX, p. 198, pi. XXXIIl, fig. 15, pi. XXXV, fig. 2 (1924). 



3) Tate, R. — Proc. Malacol. Soc. London, II, p. 182, textfigure (1897). 



SIBOGA-EXPEDITIE LIIIC. II 



