80 MONOMYARIA. SPONDYLUS- 
Genus XXIII]. — GRYPHA A. — Lamarck. 
Generic Character. — Shell free, inequivalve, upper valve 
small, flat, and acting apparently as a lid to the under one, 
which is large, concave, and arcuated ; with an incurved 
prominent umbo ; hinge destitute of teeth, with a curved 
depressed area ; provided interiorly with one muscular im- 
pression. 
Gryphea incurva. Plate VIII. fig. 23. 
This species is found in the Lias of Yorkshire, and South of England, 
various parts of Scotland, and in the inferior Oolite of France and Germany. 
The shells of this genus are extensively scattered through different rocks of the 
Cretaceous group, namely, upper and lower Greensand, Speeton Clay, and 
Chalk of all countries, as well as in the rocks of the Oolitic series. __ 
The genus is only known in a fossil condition. The species have a con- 
siderable affinity to the Ostreea, but are at once distinguished by their more 
regular form, and remarkable curvature of the beak. 
TRIBE TI.— PECTINIDES. 
Ligament placed interiorly, or partly so ; shell in general 
regular, compact and not foliaceous. 
Genus XXIV. — SPONDYLUS, — Linneus. 
Generic Character. — Shell inequivalve, subirregular ; 
umbones unequal, and distant, separated from each other by 
a triangular, flat area, and provided with small auricles on 
each side ; hinge of the lower valve with two very strong 
and greatly recurved teeth, separated by a deep central pit, 
which is the termination of a groove emanating from the 
point of the flattened area; this pit is for the reception of 
the ligament ; and two lateral hollows for receiving the 
teeth of the upper valve; the hinge of which is furnished 
with two strong reflected lateral teeth, and two intermediate 
cavities for receiving the teeth of the lower valve; the 
ligament pit is in both valves, and the ligament is for the 
most part internal, but is also external; muscular impres- 
sion single, suborbicular, and somewhat lateral ; the pallial 
presrion being eontinuous with, and surrounding the 
other. . t 
Spondylus crassicosta. Plate VIII. fig. 18. S. trun- 
cata, fig. 11. 
The Spondyli are marine shells, and inhabit the warmer portions of the 
globe ; they are conspicuous for the beauty of their colours, and their remark- 
able forms, which are generally somewhat irregular, and usually attached to 
