16 MOLLUSCA FROM THE GREAT OOLITE. 



Testa convexd oblique-ovatd, auriculis parvis subcequalibus, umbonibus prominulis, costis 

 {circa 18), radiantibus equalibus rotundis, distantibus, interstitiis planis, latis et lavigatis. 



Shell convex obliquely ovate, auricles small, nearly equal, umbones prominent, costae 

 (about 18), radiating, equal, rounded and distant, the interstitial spaces flatteued, wide 

 and smooth. 



This shell, so characteristic of the Bradford clay of Wiltshire, occurs very rarely in 

 the shelly beds of the Great Oolite, and these are of very diminutive size. 



Locality. Minchinhampton Common. 



Avicula echinata, Soio. Tab. II, figs. 7, la. 



Avicula echinata, Sow. Min. Con., t. 243, 1819. 



— — Smith. Strat. Syst., p. 67. 



— — lb. Strata Ident., p. 26 ; Cornbrash Plate, f. 8. 

 ?Var. Avicula tegulata, Goldfuss. Petref., ii, p. 132, t. 121, f. 6. 



Testa ovato-obliqud, auriculis equalibus parvis, valvd sinistra convexd costulis radian- 

 tibus numerosis, aliis minoribus interstitialibus alternatis, et lineis transversis decussatis 

 nodis formante. Valvd altera subpland, laevigata, lineis radiantibus tenuissimis subobsoletis. 



Shell ovately oblique, auricles equal and small ; left valve convex, with numerous radi- 

 ating ribs, alternating with a smaller series in the interstitial spaces, and decussated by 

 transverse, rather distant, regular lines, which form little knots as they pass over the 

 costae ; the knots are more elevated, and closely arranged upon the anterior side of the 

 shell. The other valve is nearly flat, smooth, with very fine distant and rather indistinct 

 radiating lines. 



This species is moderately common in the shelly beds of the Great Oolite, but the 

 valves are always disunited, and its state of preservation very inferior to specimens obtained 

 from the clay beds of the Fullers-earth, the Bradford Clay, or the Cornbrash, for its 

 vertical range is very considerable. 



Localities. Wherever the Great Oolite is shelly. Other geological positions are the 

 Fullers-earth clays, of the Cotteswolds ; likewise in the clays of the Cornbrash, the Forest 

 marble, and the Bradford clay of Wiltshire ; and also at Pavingham and other places in 

 Bedfordshire. 



Sub- Genus — Pteropern a . 



Testa subaequivalvi incequilaterd, utraque latere alatd, aid anticd brevi, posticd pro- 

 ductd, et marginatd. 



Margo cardinalis reclis, plus minusve obliquis, area ligamenti interna, elongatd, 

 margini externi paralleld. 



Cardo dentibus infra umbonem numerosis angustis parallelis et minutis antrorsum 

 vergenlibus et costis posticis clongatis margine car dinali parallelis. 



