TEREDO. CONCHIFERA. 113 



often surrounded by a common skin, and posteriorly a short 

 thick muscular foot, flattened at its extremity. 



P. dactylus, Lin. Shell oblong, with reticulated striae, which be- 

 come stronger and rougher toward the anterior, end ; produced 

 into a sort of beak in front of the hinge, with the edge thin and 

 reflected. Sometimes 2 inches long and 7 broad. Shores of Eu- 

 rope in calcareous rocks. B Penn. Brit. Zool. iv.pl. 42, fig. 1. 



P. Candida, Lin. Shell oblong, rounded at both ends, covered with 

 decussated prickly striae, strongest at the broadest end ; colour 

 white. } inch long and 2 broad. Inhabits European and Ame- 

 rican shores. B. Brown's Illust. pi. 9, fig. 6, 10. 



P. crispata, Lin. Shell oval, gibbous, rather obtuse, gaping, with 

 a longitudinal furrow in the middle, on one side of which the 

 shell is covered with muricated striae, and on the other trans- 

 versely wrinkled. 1 J to 2 inches long, and 2^ or 3 inches broad. 

 Inhabits European coasts. B. Brown s Illust. pi. 9, fig.l, 2, 3,4. 

 This and the preceding species are found plentifully in the clay rocks on the coast 

 between Edinburgh and Musselburgh. Their place may be detected by small cir- 

 cular openings on the surface. 



P. costata, Lin. Shell oblong-ovate, posteriorly rounded, with strong 

 crenulated longitudinal ribs and transverse striae; yellowish white. 

 2 1 to 3 inches long, and from 5 to 7 broad. Inhabits European 

 and American seas. Wood's Conch, pi. 15, fig. 1, 2. 



FAMILY IV. TUBICOLA. 



Shell contained in a testaceous sheath distinct from its valves, 

 incrusted entirely or in part in the wall of this tube, or pro- 

 jecting outwards. 



This group of animals, the last family of the class Conchifera, combine, like the 

 terminating and commencing families of most of the classes, with the general cha- 

 racters of the group, others apparently unconnected with it. It is singular, says 

 Lamarck, to find a bivalve shell inclosed in a testaceous tube, and more singular 

 still to find it incrusted on the walls of this tube, or forming an elementary part of it. 

 But the common character of having two equal and similar valves connected by a hinge, 

 seems to connect them with the Conchifera. The animals of this family are all borers, 

 and perforate sand, stones, wood, and even the thick shells of other species. 



Gen. 55. TEREDO, Lin. 



Animal much elongated, vermiform, covered with a testaceous 

 tube, perforating wood ; projecting anteriorly two short tubes 

 and two opercular bodies adhering to the sides of the tubes, 

 and having posteriorly a short muscle covered by a bivalve 

 shell. Tube testaceous, cylindrical, tortuous, open at both ex- 

 tremities, and covering the animal. Shell bivalve, placed pos- 

 teriorly, and without the tube. 



The shell of the Teredines is composed of two valves, which in the common 

 species are almost lozenge-shaped, concave, and each furnished with a subulate piece 

 within. They do much injury to the timbers of ships, perforating them in all direc- 

 tions and rendering them unserviceable. 



T. navalis, Lin. Testaceous tube subcylindrical, thin and smooth, 

 striated in various directions ; two short accessorial appendages in 



VOL. II. H 



