234 FOSSIL SHELLS OF THE CRAG. 



I consider this a distinct species, from its obliquity and 

 general uniformity of character : when compared with the last 

 species, it is thinner, the hinge never so broad, and the um- 

 ho is but slightly prominent ; externally it is covered with 

 numerous fine strice ; the chevron-formed lines are eight or 

 nine in number, and deeply impressed. 



At the above locality these shells are very abundant and in 

 good preservation, the valves being frequently united, an un- 

 common occurrence with the bivalves found in any other lo- 

 cality of the red crag. If this really be a distinct species 

 (and I have given my reason for thinking it such), the dura- 

 tion of its existence was very short, the creation and extinc- 

 tion appearing to be limited to the period of the red crag. 



Pectunculus pygmcBus. PI. xiii. fig. 5. 



Pectunculiis pygmmts , Philippi, ' Moll. Sicil.' page 63, tab. 5, fig. 5. 



Shell rhomhoidal, inequilateral, oblique, ventricose, ligamental area with a 

 central deltoidal pit ; hinge teeth about ten, margin crenulated. Lon- 

 gitudinal diameter i ; transverse diameter ^ of an inch. 



Coralline crag, Sutton. 



Abundant. This shell appears to agree with the descrip- 

 tion and figure above quoted. The four teeth on the anterior 

 side are nearly horizontal, while four of those on the other 

 are vertical and very prominent, the two most lateral, angu- 

 lated. The arrangement of the teeth in the figure of the Si- 

 cilian shell is indistinct, and the description merely says, — 

 " dentes circa decem." The shell is striated and sulcated, 

 by which the exterior has a cancellated appearance ; the 

 longitudinal st^'ice are visible internally ; a few on the ante- 

 rior angle are more conspicuous ; the margin is crenulated all 

 round. This species, and a few others, have been put into a 

 separate genus [Limopsis), in consequence of the central del- 

 toidal pit in which the ligament appears to have been placed, 

 instead of being spread over the whole area; between the 

 hinge line and umbo a small opening is visible in those spe- 

 cimens where the valves are found united. Pectunculus na- 

 nus of Deshayes differs in the arrangement of the teeth, and 

 in having the longitudinal stricB more strongly marked : his 

 figure does not show the deltoidal pit. 



(To he continued.) 



