418 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



racters of the shell : the casts are composed of a fine yellowish ferru- 

 ginous sand. 



Arca stjbrostrata. 



Figs. 8, 9. 



A. testa subinaequivalvi, ovata, insequilaterali, costato-radiata, latere antico brevi, 

 rotundato, postico longiore subrostrato, costis radiantibus, anticis prsecipue sub- 

 rugosis ; interstitiis concentrice striatis. Long. 1-2, lat. 075, alt. 0*8 poll. 



Very like Arca antiquatay but its general form is different, owing 

 to the posterior part being more acuminated ; it is moreover slightly 

 inequivalve. 



Pecten Pandora, Desh. 



Fig. nost. 22. 



P. testa subsequivalvi, subasquilaterali, suborbiculari, squamiilis minimis con- 

 fertissimis rugosa, radiatim costata et striata, costis alterius valvse 14-15 

 majusculis, inaequalibus ; alterius 15, subaequalibus ; omnibus, interstitiisque 

 longitudinaliter striatis, striis prope marginem ventralem omnibus confertissime 

 squamulosis ; auriculis magnis, radiatim striatis et squamulosis. Long. 3*0, lat. 

 1-0, alt. 2-8 poll. 



This is probably the Pecten PandorcB described and figured in the 

 * Expedition scientifique de Moree ' by Deshayes, but we have thought 

 it necessary to give another representation of it, because our speci- 

 mens are so much larger than his representation. It is evidently quite 

 distinct from P. pleheius, Brocchi. 



Pecten tenuisulcattjs. 



Figs. 19, 20, 20 «. 



P. testa insequivalvi, sequilaterali, tenui, cornea, Isevi, valva altera plano-convexi- 

 uscula, costis radiantibus 14-15, rotundatis, angustis, interstitiis latioribus ; 

 altera convexa radiatim tenuiter sulcata, costis interstitialibus leviter elevatis. 



This species is nearly similar in general form to Pecten Beudanti 

 of Basterot, and it has been thought to be identical with it, though it 

 may very easily be distinguished by the smooth convex valve not 

 being deeply grooved, as in that species. The short character given 

 by Basterot is not sufficient to enable us to form any idea of the spe- 

 cies independently of the figure, which may be seen in the ' Mem. de la 

 Soc. d'Hist. Nat. de Paris,' tome ii. pi. 5. fig. 1. A, B, C. His words 

 are : "P. testa lamellis acutis, transversis, confertis ; striis intercos- 

 talibus nullis ; costis 17-18;" which however are sufficient to prove 

 our P. tenuisulcatus to be quite distinct. 



Pecten conjux. 



Fig. 17. 



P. testa aequilaterali, inagquivalvi, valva altera plana, prope umbonem subconcava, 

 concentrice tenuissime striata, radiatim costata, costis 15-18 rotundatis, inter- 

 stitiis paululiim latioribus. Long. 3*0, alt. 2*5 poll. 



We possess the flat valve alone of this species, which resembles the 

 same valve of Pecten medius ; the ribs in this species are however 

 more numerous and the interstices nearly equal, whereas in P. medius 

 the interstices are much broader than the ribs, and there is moreover, 



