192 J. S. GARDNER ON BRITISH CRETACEOUS PATELLID^ ETC. 



11. On British Cretaceous Patellidjs and other Families of 

 Patelloid Gastropoda. By J. Starkie Gardner, Esq., F.G.S. 

 (Read January 24, 1877.) 



[Plates VII.-1X] 



A study of this group of Cretaceous Gastropoda, commenced some 

 twelve months since, brought to light unexpectedly so many forms 

 new to our Cretaceous series, some of the genera to which they are 

 referred having, indeed, never before been found fossil, that I have 

 deemed the result of sufficient importance to form the subject of a 

 paper which I now lay before this Society. Conical or patelloid 

 shells make their appearance amongst the earliest known Mollusca ; 

 and from them seem to have been differentiated the convoluted 

 forms represented by Bellerophon : in the earliest times these two 

 typical forms can hardly be separated one from the other, being 

 linked together by spirally twisted capuliform shells. So impressed 

 does Pictet seem to have been with this that he, in his great work 

 the ' Terrains Cretaces de Ste. Croix,' includes Bellerophina in the 

 Fissurellidae. The families, species of which are here noticed, have 

 been unusually persistent in form, having come down, in some cases, 

 almost unchanged, even specifically, to the present day. The aspect 

 of the group is therefore more recent in appearance than that of 

 any other group of Gastropods from rocks of the same age. Although 

 a considerable advance is here made in our knowledge of these 

 families, from these particular rocks, yet the number of species de- 

 scribed from single specimens tells us unmistakably how much 

 more remains to be learned, and the inference is forced upon us 

 that we must still possess, though undiscovered, a far greater variety 

 of representatives of these mollusca. By the absence of many 

 genera from our Cretaceous rocks which are found in earlier rocks, 

 such as Rimula, or in contemporaneous rocks of other countries, 

 such as Fissurella, Parmopliorus, Infundibulum, Galerus, and the 

 upper valves of Hipponyx, this inference is greatly strengthened. 



The study of these families is perhaps of more importance to the 

 geologist than that of most others of the Gastropoda, as the depth 

 at which each form lived is approximately defined, and their pre- 

 sence or absence is therefore of assistance in understanding the 

 physical conditions under which marine strata have been deposited. 

 For instance, from the complete absence of fissured forms from the 

 Gault andGreensand of Polkestone, Cambridge, and Blackdown, while 

 they are abundantly represented elsewhere in rocks of approximately 

 the same age, we may infer that these seas were shallow. Further 

 remarks are appended to some of the specific descriptions ; especially 

 noteworthy are some remarkable cases of mimicry among the 

 CalyptraBidae. A table of genera and species is appended. In this 

 table the * signifies that the genus is altogether new in Cretaceous 

 rocks ; f , new to Europe ; N, that the species is new. In the 



