BIVALVIA. 71 



In the young state the specimens have fewer teeth, and the shell, as before stated, 

 is less oblique, resembling the young of Pectuncidus, from which it may be distinguished 

 by its smooth and acute margin at all ages ; while in the very small or young specimens 

 of P. glycimeris the crenulated edge may be always seen. Some specimens are more 

 tumid than others, but none are much inflated, and the exterior is smooth and perfect, 

 except where it has been eroded, when the rays are more displayed, giving it there a 

 granulated or decussated appearance, like Area aurita of Brocchi, from which it appears 

 to differ only in size. 



The remains of red-coloured bands may be seen upon some specimens as if the 

 shell had been so ornamented when in a living state, or perhaps it was of one 

 uniform colour, a part of which only has been abstracted. 



Trigonocodia Goldfussii, Nyst, from Kleyn Spauwen, much resembles our shell, but 

 is probably specifically distinct; it has its margin obsoletely crenulated, and the 

 denticles are more numerous, with a slight difference in their arrangement. 



Limopsis pygmjEA, Philippi. Tab. IX, fig. 3. 



Pectunculus pygm^eus. Phil. En. Moll. Sic. vol. i, p. 63, t. 5, fig. 5, 1836 ; not Lamarck. 



— — Id. - - - vol. ii, p. 45, 1844. 



— — S. Wood. Mag. Nat. Hist., New Series, vol. iv, p. 234, pi. 13, 



fig. 5, 1840. 



— — Id. Catalogue, 1840. 



— — Gold/. Pet. Germ. vol. ii, p. 162, t. 126, fig. 11, a—c. 



— — Morris. Cat. Brit. Foss., p. 97, 1843. 



Trigonoccelia decussata. Nyst et West. Nouv. Rech. Coq. Foss. d'Anv., p. 12, No. 29, 



pi. 2, fig. 16, 1839. 



— — Nyst. Coq. Foss. de Belg., p. 245, pi. 18, fig. 7, a— d, 1844. 

 Limopsis pygm^a. Sism. Syn. Meth. Ped. Foss., p. 15, 1847. 



Spec. Char. Testa minutd, obliqud, incequilaterd, subtrapeziformi, gibbosd, crassd, 

 auriculatd; transversim sidcatd, striis radiantibus tenuissimis, subobsoletis ; margine 

 crenulato, dentibus circa decern. 



Shell small, oblique, inequilateral, subtrapeziform, gibbous, thick, and strong; 

 hinge line straight, furnished with about ten teeth ; externally covered with fine and 

 nearly obsolete radiating striae, crossed by more distant and distinct lines of increase ; 

 margin crenulated. 



Longest diameter, \ of an inch. 



Locality. Cor. Crag, Sutton. 



This species, as far as I know, is restricted to a single locality, where it is one of 

 the most abundant shells, and the two valves are often found united. I have little 

 doubt it is the same as Philippi's Sicilian fossil, judging from the figure he has given ; 

 the Belgian shell appears rather larger or badly represented, but from description it is 

 probably the same. Our shell may be further described as being very tumid, the 

 depth of the valves united equals the width of the hinge line ; its dental formula 



