BIVALVIA. 79 



and regularly decussated exterior, but with a small and narrow ligamental area. Area 

 nodidosa, Brocchi, seems to belong to our present species, as does also, in all probability, 

 the one figured and described under that name by Dubois, judging from his short 

 description and small figure. 



ARCA PECTUNCULOTDES, Scacchi. Tab. X, fig. 3, a b. 



ARCA PECTUNCULOIDES. Scac. Ann. Civ. delle Due Sicil., vol. vi, p. 82, 1834, fide Nyst. 

 Scacchi, Notizia, p. 25, t. 1, fig. 12, sec. Phil. 

 Phil. En. Moll. Sic., vol. ii, p. 44, t. 15, fig. 3, 1844. 

 Jeff. Ann. Nat. Hist., vol. xix, p. 313. 

 Lovtn. Ind. Moll. Scand., p. 34, 1846. 

 ? Mich. Free. Faun. Mioc., t. 3, fig. 14, 1847. 

 Sismonda. Syn. Metli. Pedm. Foss., p. 16, 1847. 

 Nyst. Tab. Synop. des Arches Viv. et Foss., p. 54, No. 300, 1847. 

 RARIDENTATA. S. Wood. Mag. Nat. Hist., New Series, vol. iv, p. 232, pi. 13, 



fig. 4, 1840. 



Thompson. Ann. Nat. Hist., vol. xviii, p. 385. 

 S. Wood. Catalogue, 1840. 

 Morris. Cat. Brit. Foss., p. 78, 1843. 

 Forb. and Hani. Hist. Brit. Moll., vol. ii, p. 241, pi. 45, fig. 8, 



1849. 



PUSILLA. Nyst. Coq. Foss. de Belg., p. 261, pi. 20, fig. 6, 1844. 

 CUCULLCEA PUSILLA. Nyst. Rect. Coq. Foss. Prov. d'Anv., p. 14, pi. 3, fig. 55, 1835. 



Spec. Char. Testa pared, incequilaterd, ovato-rhomboided, gibbd ; striis exiguis, 

 decmsatis ; area ligamenti parvd, apicibus refleccis ; car dine recto, ntrinque tridentato ; 

 margine ventrali subsinuato. 



Shell small, inequilateral, ovato-rhomboidal, gibbous ; ornamented with fine 

 decussating striae ; ligamental area small, umbones inflected ; hinge line straight, 

 furnished with three teeth on each side ; ventral margin subsinuated. 



Largest diameter, gth of an inch. 



Locality. Cor. Crag, Sutton. Recent, Britain, Mediterranean, and ^Egean Seas. 



This elegant little shell is another species, but rarely found in the British Seas, and 

 which may perhaps be one of those we might consider to be in a specific decline, or 

 the dying out of what was once largely developed in these latitudes. In the Coralline 

 Crag at Sutton this is one of the most abundant fossils, and I have obtained the 

 separated valves by hundreds. 



It is stated by the authors of the ' Hist, of Brit. Moll.' to be slightly inequivalved. 

 In the fossil state I have never been able to obtain a specimen with the valves united. 

 There does not appear to be any doubt of its identity with the living British species, 

 and a single valve obtained from a considerable depth in the ^Egean Sea, obligingly 

 given to me by Professor E. Forbes, corresponds in all respects with the Crag shell. 



Where the specimens are so abundant, differences of form may naturally be 

 expected, some may be selected that are more elongated and less tumid than others, 



