DIMYARIA. 165 



Genus 68.— VROL AS.— LinncBus. 



Generic Character. — Animal without a tubular sheath, 

 projecting anteriorly into two united tubes, frequently sur- 

 rounded by a common skin, and the posterior extremity pro- 

 vided with a very short muscular foot, blunt at the end. 

 Shell bivalve, equivalve, transverse, gaping at both extre- 

 mities, 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, 

 which separates from the plain wrinkled half by a broad 

 furrow down the middle. Two inches long and three 

 broad. Inhabits the British coasts. 



TRIBE IV. TUBICOL^. 



Shell contained in a testaceous sheath distinct from its 

 valves, or incrusted wholly or partly in the wall of this 

 tube, or projecting outwards. 



Genus 69.— TEREDO.— LinncBus. 



Generic Character. — Animal much elongated, worm- 

 shaped, invested by a testaceous tube, and boring into 

 wood ; with two anterior, projectile, short tubes, and two 

 opercular processes, adhering to the sides of the tubes ; with 

 a posterior short muscle, protected by a bivalve shell. Tube 

 testaceous, cylindrical, and tortuous, pervious at both ex- 

 tremities, and covering the animal. Shell bivalve, placed 

 externally of the tube ; each valve provided with a subulate 

 piece within. 



Teredo navalis. — The Ship Teredo, or Ship-worm. 

 Plate XVIII. figs. 18 to 22. Cylindrical, taper, smooth, 

 white, somewhat flexuous, finely striated longitudinally. 

 Inhabits the European seas, in timber. 



