DIMYAIHA. 145 



TRIBE III. PIIOLADARIA. 



Valves with accessory pieces ; or gaping considerably ante- 

 riorly. 



Ge7ius 67. —G ASTRO CH(ET^A.Spengler. 



Generic Character. — Equivalve, somewhat wedge-shaped-, 

 w^ith a very large, oval, oblique, anterior opening betwixt the 

 valves, the posterior extremity nearly close ; hinge linear, mar- 

 ginal, and without teeth. 



Gastrochoena modiolina. — The Modioliform GASTROCHffiNA. 

 Plate XVIII. fig. 16. Oval, thin, brittle, gaping at the side ; 

 of a light reddish-brown ; inside bluish-white. Three-fourths 

 of an inch long. Inhabits the British coasts ; boring into hard 

 substances. 



Genus 68 — PHOLAS.— iirt»ff?/5. 



Generic Character. — Animal without a tubular sheath, pro- 

 jecting anteriorly into two united tubes, frequently surrounded 

 by a common skin, and the posterior extremity provided with a 

 short muscular foot, flattened at its extremity. — Shell bivalve, 

 equivalve, transverse, gaping at both extremities, with various 

 accessory pieces either on the hinge or below it ; inferior margin 

 of the valves inflected. 



Pholas crispatus. — The Curled Pholas. Plate XVIII. 

 fig. 17. Somewhat oval ; reticulated on the anterior half, and 

 separated from the plain wrinkled half by a broad furrow down 

 the middle. Two inches long and three broad. Inhabits the 

 Eritish coasts. 



TRIBE IV. TUBICOLA. 



Shell contained in a testaceous sheath distinct from its valves, 

 incrusted wholly or partly in the wall of this tube, or projecting 

 outwards. 



