186 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Nov. 21, 



Gervilia Fittoni, n. s. Pl. XXIII. fig. 3-6. 



Shell elongated, subrhomboidal, veiy oblique, nearly equivalve ; 

 posteriorly produced and flattened ; anterior wing short, tumid and 

 indistinct. Very slight sinus for the passage of a byssus, which is 

 most marked on the left yalve. Dorsal margin straight ; hinge-area 

 very deep, and enlarging anteriorly eyen in front of the umbo : liga- 

 mental sockets very unequal and usually few. Irregular dental 

 callosities on the hinge-area ; those before the umbo nearly perpen- 

 dicular, those behind it sloping. 



Length 1^ inch ; breadth 3^ inches ; height f of an inch. 



Abundant in subcretaceous limestone between Torres Vedras and 

 Sobral. 



Very closely resembling G. Sohralensis, this species is distinguisheci 

 by the perpendicular position of the anterior teeth, and by the greater 

 height of the hinge-area, which continues to increase in height quite 

 to the anterior extremity ; whereas in most species of the genus its 

 height is greatest at the umbo. The ligamental sockets in old shells 

 are usually three ; but one specimen, fig. 5, has them more nume- 

 rous, though in other respects agreeing with this species. 



Fig. 3. Exterior. 



Fig. 4. Interior of another specimen. 



Fig. 5. Interior of a variety with the ligamental sockets nnmerons. 



Fig. 6. Hinge-area of a young shell. 



I have named this species after Dr. Fitton, to whom all geologists 

 are indebted for his labours on the subcretaceous strata, and to whose 

 friendship I owe more than I can here venture to express. 



Gervilia Sobralensis, n. s. Pl. XXIII. fig. 1 & 2. 



Shell elongated, very oblique, subtriangular, tumid, nearly equi- 

 valve ; produced posteriorly into a blunt point ; anterior wing 

 tumid, and faintly separated by a shght diagonal depression, which 

 is most marked on the right valve. 



Hinge-area equal to about half the breadth of the shell ; with two 

 ligamental sockets in young, and four in old shells, of very unequal 

 size. Hinge-teeth numerous, very unequal, and radiating from the 

 umbo ; those in front of the umbo sloping forward at angles from 

 40° to 60°, those behind the umbo sloping backward from 10° to 

 30° with the hinge-line. As the animal grows old, shelly matter is 

 deposited over those parts of the hinge-area which are not pro- 

 tected by the ligament, and the teeth are nearly concealed except in 

 the ligamental sockets, where their traces are seen under the Hga- 

 ment, and along the inner margin of the hinge-area. 



Sinus for the escape of the byssus very slight. 



Length 1^ inch ; breadth 3 inches ; thickness 1;^ inch. 



Abundant in subcretaceous limestone between Sobral and Torres 

 Vedras. 



The characters by which this species is most readily distinguished 

 are the short tumid anterior wing, almost continuous with the rest of 



