114 MOLLUSCA FROM THE GREAT OOLITE. 



Panopaa longa, Buvig., 'Geol. de la Meuse, Atlas,' pi. 7, fig. 1, 3, to which, in other 

 respects, it has a general resemblance. 



The Arcomya calceiformis, Ag., 'Etud. Crit. Myes.,' p. 176, tab. 9, fig. 7, 9, from the 

 ferruginous Oolite of Moutiers, is a different species of the same group or sub-genus, and 

 must be distinguished from our shell, which has the priority of name. 



Height, 21 lines ; length, 43 lines ; diameter through both the valves, 14 lines. 



Position and localities. The geological range of this species is considerable ; in the 

 Cotteswolds it occurs in the upper beds of the Inferior Oolite, in the fullers' earth, also 

 in hard pale coloured sandstone near to the base of the Great Oolite ; it occurs also in 

 the Cornbrash of Chippenham, Malmesbury, and Cirencester; and at the latter three 

 localities it is not uncommon. Professor Phillips records it in the Inferior Oolite of Blue 

 Wick, and in the Kelloway rock of Scarborough. 



Myacites dilatus, Phil. sp. Tab. X, fig. 5 a, b. 



Mya dilata, Phil. Geol. York., 1, tab. 11, fig. 4. 



— — Morris. Catal. Brit. Foss., p. 92. 

 Sanguinolaria (?) dilata, Buchncm and Strickland. Geol. Chelt., pi. G, fig. 1. 

 Panopcea dilatata, jyOrb. Prodr. de Paleont., 10 etag. No. 216. 



Testa elongatd, antice compressd, postice subcglindricd, dilata et truncatd ; umbonibus 

 antemedianis, parvis, comprcssis ; aperturd anticd angustd ; posticd magna saperne 

 elongatd ; margine superiori concavo, inferiore subrecto ; lateribus plicis irregularibus 

 magnis, angulo postico flecto ; superficie granulis regularibus serialibus radiantibus 

 dispositis. 



Shell elongated, anterior side compressed, posterior side nearly cylindrical, dilated and 

 truncated at the extremity; umbones anterior to the middle of the valves, small, and 

 compressed ; anterior aperture narrow ; posterior aperture large, suborbicular, but ex- 

 tending along the superior border almost to the ligament ; superior border concave ; 

 inferior border nearly straight ; the sides of the shell with a few large irregular longi- 

 tudinal plications, which are bent upwards posteriorly at a considerable angle; the 

 radiating lines of granules are rather large, and most conspicuous upon the posterior side. 



The compressed anterior side of the shell is strikingly contrasted with the posterior 

 expansion. Much variation exists in the proportions of its posterior elongation, and the 

 latter border is sometimes reflected, the more aged specimens being the most elongated : 

 the figure in the ' Geology of Cheltenham' represents the most shortened phase of form. 

 The Great Oolite specimens are small ; they have not occurred in the shelly beds, but in 

 some imperfectly slaty deposits near to the base of the formation. The species also occurs 

 in the fullers' earth, and in the upper portion of the Inferior Oolite, the latter rock 

 producing by much the finer specimens. The punctations upon the granules appear to 

 resemble those of the recent Anatina hispidula, and in like manner probably gave in- 



