386 SPECIAL GEOLOGY. 



DESCRIPTION OF FIG. 271. 



1. Corbis corrugata, from the sand-rock, Atlierfield : the figure is one-half the size in 



linear dimensions of the original. 

 '2. Trigonia caudata. from the sand-rock, Atlierfield. 



3. Gervillia anceps, from the Cracker Rocks, Atlierfield ; a, denotes the markings of 



the hinge, which are seen in consequence of the valves being slightly displaced. 

 It is represented half the size linear of the original. These shells are often 

 much larger, and more elongated than in the figure. 



4. Venus striato-costata ; a small shell, common in the Cracker Rocks at Atherfield 



the figure is twice the size of the original in linear dimensions. 

 6. Area Raulini, from the sand-rock, Atherfield. 



6. Perna Mulleti, from the lower beds of sand in conjunction with the wealden, 



Sandown Bay ; the figure is but half the size of the original : a, the structure 

 of the hinge; by comparing this figure with a, No. 3, the difference of the hinge 

 in the genera' Perna and Gervillia will be recognised. This large and 

 remarkable shell is highly characteristic of the lower beds of the greensand. 



7. Venus parva, from Shanklin Cliff. 



DESCRIPTION OF FIG. 272 



1. Thetis minor, from the ferruginous sand-rock at the base of Shanklin Cliff. 



2. Another view of the same, to show the beaks and hinge-line. 



3. Gryphea sinuata, represented one-fourth the natural size ; it is often found much 



larger. From the greensand at Shanklin, Ventnor. Sandown, &c. 



4. Tornatella albensis, from the Cracker Rocks, Atherfield. 



5. Terebralula sella ; an abundant shell in the sand at Atherfield. 



6. Nucula scapha, from the sand-rock, Atherfield. 



The three following shells are embedded in a fragment of the Cracker Rock, from 

 Atherfitld. 



7. Natica rotundata. 



8. Pterocera retusa. 



9. Rostellaria Robinaldini. 



10. Cerithium turriculatum, from Atherfield. 



11. Ancyloceras gigas, from Atherfield. The figure is but one-third the size, linear, of 



the original. 



This fossil is often found two feet in length, associated with Ammonites equally 

 gigantic. 



PISHES OF THE CHALK. The most interesting remains, 

 exhumed from the Sussex chalk, consist of numerous admi- 

 rably preserved fishes, which have furnished subjects for a 

 portion of the work of Professor Agassiz.* We select Osme- 

 roides Mdntellii, as an illustration (fig. 273.) : 



* The following is the eulogy of Agassiz on this highly interesting collec- 

 tion : " Tout le monde sait que le Musee de M. le Dr. Mantell est une 

 collection classique pour la craie et la formation Veldienne. Les soins minu- 

 tieux que M. Mantell a donne, depuis bien des annees, a ces fossiles, les ont 

 rendus plus parfaits que tons ceux des autres musees; car, souvent il est 



