﻿1861.] 



PItESTWICn BOULDEK-CLAY. 



449 



No. Species. 



Bivalves. 

 Cardium edule, var. 



4. Corbiila nucleus 



5. Cyprina Islandica f 



*6. Cyrena fluniinalis, Midler . 



7. Mactra solida 



8. subtruncata 



■ — , var. 



9. Mya tnuicata 



10. Mytilus edidis 



11. Nucula nucleus 



12. Ostrea edulis 



18. Pbolas crispata 



14. Tellina solidula 



15. Venus striatula 



Remarks on the comparative 

 frequency, &c. 



. An estuarine or brackish-water form ; 

 more produced at the anterior side 

 and thinner : less frequent than the 

 last *. 



. Rare. 



. A fragment. 



. Abundant. Corhicula fluminalis of 

 conchologists. Some specimens are 

 larger than recent ones of the same 

 form. 



. Not common : a small variety, inter- 

 mediate between this species and 31. 

 elliptica of Brown, which I consider 

 a variety of it. 



. Not common. The lateral teeth in this 

 and the last species are perpendicu- 

 larly striated, as in Cyrena. 



. Rare. The Irish deeply striated form. 



. Two fragments. 



. A few fragments. 



. A fragment. 



. Rather common : not of any size. Ap- 

 parently an estuarine form. 

 . A few fragments. 

 . Very abundant, but not of any size. 

 . A single valve. 



Univalves. 



16. Buccinum imdatum Very abundant : a northern form, hav- 



ing the ribs more obliquely carved. 



17. Dentalium entale Not common. 



18. Fusus gracilis, Da Costa .... A fragment. This is the F. Islandicus 



of Forbes and Hanley, who appear 

 to have mistaken Da Costa's species 

 for the F. Islandicus of Chemnitz. 

 These species are very distinct. 



19. antiquus,var.despectus . An immature specimen and a fragment 



of another. In this country it occurs 

 only in the south of Ireland and in 

 Zetland. 



arnination just made by Mr. Jeffreys of my original collection, as well as of a fur- 

 ther series collected by Mr. Smith, and sent me only a few days since. It will be 

 seen by my observations which follow those of Mr. Jeffreys, and which remain 

 as they before stood, that our conclusions, which are based upon independent 

 grounds, are in very close agreement. — 21st Oct. 1861. 



* In Mr. M c Andrew's Report to the British Association, in 1856, on certain 

 dredging operations, he says (p. 134), " Near Tunis a narrow neck of land divides 

 the bay from a shallow salt-water lake, at the head of which the city of Tunis is 

 situated ; on the one side of this neck of land (that facing the bay) all the speci- 

 mens of Cardium edide were strong, triangular, and with few ribs, while on the 

 other side, towards the lake, they were thinner, wider, and much more numerously 

 ribbed. The northern varieties attain the largest size." — J. Gr. J. 



t This may have been washed out of some of the lower beds of the Boulder - 

 clay, where such fragments are often common. So also the fragment of Astarte 

 com/pressa. — J. P. 



