BIVALVIA. 83 



surface can be examined and compared, the minute, crowded pattern upon M. sinistra, 

 with the widely separated lines of granules upon M. decurtatum. 



Geological Positions and Localities. The Cornbrash of Scarborough ; in the col- 

 lection of Mr. Leckenby. In Switzerland M. Agassiz records it from the same geological 

 position (calcaire roux-sableux) at Goldenthal, Soleure ; also in the Bernese Jura. 



MYACITES MODICA, Bean, sp. Tab. XLIII, figs. 1, 1 a. 



MYA MODICA, Bean. Mag. Nat. Hist., 1839. 



Testa-ovato elongata suldepressa, umbonibus subdepressis antemedianis, margine antico 

 producto, rotundo, poslico oblique declivi subrccto, margine inferiore elliptico curvato, area 

 ligamenti lanceolata lata, sitbdepressa, marginilus acutis, valvis lateribus concentrice delicate 

 plicatis ; lineis radiantibus granulatis, subtillissimis dense instructis. 



Shell ovately elongated, rather depressed ; umbones antero-mesial, rather depressed ; 

 anterior margin produced, rounded; posterior margin more lengthened, nearly straight, 

 sloping downwards obliquely, lower border curved elliptically ; the granulated test consists 

 of extremely delicate, very densely arranged, radiating lines, visible only under a magnifier; 

 the concentric plications are numerous and faintly traced, so that the surface is smooth ; 

 the valves are close-fitting, or have no perceptible aperture at either of the extremities. 



Length, 2 inches; height, 1^ inch; diameter through both the valves, i inch. 



The general figure and aspect of this species renders it easy to distinguish from other 

 examples of the genus. 



Geological Position and Locality. The Cornbrash of Gristhorpe Clio's, in which it has 

 occurred very rarely ; Mr. Leckenby 's collection. 



ANATINA (CEREOMYA) SILIQUA, Ag. Tab. XXXV, fig. 15. 



SANGUINOLAKIA UNDULATA, Phil. Geol. York., i, pi. 5, fig. 1, non Sow. 

 CERCOMYA SILIQUA, Ag. fit. Crit. Myes., p. 148, tab. 11 a, figs. 9 13. 



ANTICA, Ag.l Ib., p. 147, tab. 11, figs. 1618; tab. ll<z, 



figs. 1416. 



AXATINA BELLONA, D'Orb. Prod., i, p. 336, 12 et., No. 132. 

 UNDATA, Id. Ib., p. 361, 13 et., No. 221. 



SANGUINOLARIA CNDULATA, Quenstedt. Der Jura, p. 508, t. 68, fig. 9. 

 ANATINA UNDULATA, Leckenby. Proc. Geol. Soc., vol. xv, 1858. 



Testa transverse elongata inaquilatera wnbonibvs subanticis parvis acutis, postice 



