ol 



another, resembling it in form, but very distinctly marked with longi- 

 tudinal and transverse rugae, much like the Gloucestershire limpet. I 

 observe the same characters in another fossil patella from the valley of 

 Ronca, in the Veronese. 



This genus presents the best place in which I can notice the remark- 

 able limpet-like shell described by Da Costa, who never saw but four 

 that were entire, or nearly so. He places it among the patellae; and 

 says : " These limpets are very large ; and, like the Concholepas, resem- 

 ble a single shell of a bivalve. They seem to be of two kinds, and are 

 more irregular than that shell ; and, instead of being sulcated length- 

 wise, are circularly wrought, or in a transverse manner, with very high 

 irregular ridges, not thickly, but rather thinly, set. The shells are very 

 thick : one sort is high or copped, the other is broad or flattish." Ele- 

 ments of Conchology, p. 142. The specimens which I possess of this fos- 

 sil are not sufficiently illustrative of its form. I have however given a 

 figure of one of them, which was found at Pangbourn, in Berkshire, 

 Plate V. Fig. 3. 



III. Fissurdla. A buckler formed univalve, without spire : the ver- 

 tex perforated, with an ovate or oblong opening. 



The species which I have obtained from the Essex cliffs nearly resem- 

 ble the F. labiafa, Lam. 



IV. Emarginula. An obliquely conical univalve, the vertex inclined, 

 and the posterior margin slit or notched. 



I have repeatedly found a species of this genus in, the Essex cliff, 

 which, in its elegantly reticulated or cancellated surface, its reclined 

 vertex, and its size, agrees with P. fissura, as figured by Pennant, 

 PL xc. Fig. 152 ; and by Lister, Tab. DXLIII. Fig. 28, who describes 

 it as Patella exigua, alba, cancellata, fissura notabili in margine. 



Three species are described by Lamarck : E. costata, E. Clypeata, and 

 E. radiola. 



V. Crepidula. An oval or oblong vaulted univalve, with its apex in- 

 clined to one end, and its cavity partially divided by a horizontal plate. 



