BIVALVIA. 83 



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

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



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

 lection of j\Ir. Leckenby. In Switzerland ]\I. Agassiz records it from the same geological 

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



Myacites modica. Bean, sp. Tab. XLITI, figs. 1,1a. 



Mya modica, Bean. Mag. Nat. Hist., 1839. 



Testa-ovato elongata snldepressa, nmlonihus siihdepressis antemedianis, maryine antico 

 producto, rofundo, postico oblique declivi siibrecto, marcjine inferiore eUiptico curvato, area 

 ligament i lanceolata lata, subdcpressa, marginibusacutis,valvislaterihus concentrice delicate 

 plicatis ; lineis radiantibtis granulatis, stibtillissimis dense instriictis. 



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, | 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 Cliffs, in which it has 

 occurred very rarely ; Mr. Leckenby's collection. 



Anatina (Cereomya) siliqua, Jg. Tab. XXXV, fig. 15. 



Sanguii^olaria undulata, Phil. Geol. York., i, pi. 5, fig. 1, non Sow. 

 Cekcomya siliqua, Ag. Et. Crit. Myes., p. 148, tab. 11 a, figs. 9 — 13. 



— ANTicA, J^.? lb., p. 147, tab. 11, figs. 16—18; tab. lie, 



figs. 14—16. 

 Anatina Bellona, D'Orb. Prod., i, p. 336, 12 et., No. 132. 



— xjndata. Id. lb., p. 361, 13 et., No. 221. 

 Sanguinolaria undulata, Quenstedt. Der Jura, p. 508, t. 68, fig. 9. 

 Anatina undulata, Lecltenby. Proc. Geol. Soc, vol. xv, 1858. 



Testa transverse elongata inaquilatera umbonibus subanticis parvis acutis, postice 



