338 GINGLYMACONCHA. PECTUNCULIDZ. 
Inhabits the British Sea in deep water, found immersed in 
the holes of rocks very abundantly. Dr. Turton supposes that 
they perforate the rocks themselves: all those that I have 
seen were in masses of rock perforated by Pholades ; I there- 
fore cannot agree with him in this opinion. 
This species is most decidedly distinct from the Arca lactea 
of Linneeus : of this I am well assured, having compared it with 
the 4. laetea in the Museum of my worthy friend Le Cheva- 
lier De Lamarck, taken in the Mediterranean, where Linnzus 
says that it inhabits. 
FAMILY XIV. PECTUNCULID. 
Shells orbicular, equivalve, nearly equivalve shut; the 
hinge arched, with numerous oblique teeth, the middle ones 
obsolete ; the cardinal ligament external. 
Genus 67. PECTUNCULUS. 
Glycymeris, Da Costa. 
Pectunculus, Lamarck, Cuvier, Say, &c. 
Axinea, Poli. 
The shells orbicular, sublenticular, equivalyed, nearly equi- 
lateral and completely shut ; the hinge arched, with numerous 
oblique teeth placed in an alternating series; the middle one 
obsolete ; the ligament external. 
The foot is very large, its inferior margin doubled. 
1. PecruNcUuLUS GLYCYMERIS. 
Shells with their valves orbicular, transverse, nearly equi- 
lateral, longitudinally suleated and striated with divaricating 
strie ; the older valve turgid and very thick, painted with 
obscure concentric zones. Length three inches and a half; 
height three inches and a quarter. 
Arca Glycymeris, Knorr. Vergn. vi. t. xiv. f. 3; Linn. Syst. 
