66 The Shipworm. [Sess. 



food. The Teredo and Pholas belong to the class Lamelli- 

 branchia (Lat. lamella, a thin plate ; and Gr. bragchia, a gill) — 

 their respiration, which is a characteristic feature, being per- 

 formed by gills of vascular plates of membrane attached to 

 the inner surface of the mantle. This class of acephalous 

 or headless molluscs is further represented by such familiar 

 examples as oysters, cockles, and mussels. They present, 

 as a whole, a somewhat uniform structure, so that although 

 numerous, their further subdivision is not the result of 

 broadly marked characters. The latest classification refers 

 the Teredo to the order Isomya, sub-order Sinupallia, and 

 family Pholadacea, of which family the Pholas is the type. 

 The majority of the Lamellibranchia may be said to be borers, 

 so far as the power of burying themselves in sand, clay, mud, 

 or gravel can give them a claim to such an appellation. The 

 chief points in which they vary are five : — 



1. In the structure of the branchial plates. 



2. In the presence of one or two chief muscles or ad- 

 ductors, the fibres of which run across the body from one 

 valve of the shell to the other. 



3. In the greater or less development of the posterior por- 

 tion of the mantle -skirt, so as to form a pair of tubes or 

 siphons, by one of which water is introduced into the sub- 

 pallial chamber, whilst it is expelled by the other. 



4. In the perfect or deficient symmetry of the two valves 

 of the shell ; and 



5. In the development of the " foot " as a disc-like crawling 

 organ. 



The Teredo, then, is a much elongated and worm-shaped 

 abnormal form of a Lamellibranchiate mollusc, measuring in its 

 adult state from a few inches to over 3 feet in length, and 

 living upon the wood in which it burrows. It has a true bi- 

 valve shell at the front extremity, the valves are triangular in 

 shape, equal and right and left, very concave on the side in 

 contact with the animal, and their interior is furnished with a 

 long curved process for the attachment of the pedal muscle. 

 They are destitute of a hinge, gape at both ends, afford no 

 protection to the body, but are reduced to mere appendages of, 

 and surround, the short sucker-like foot. The portion of the 

 body behind the shell- bearing part is naked except for the 



