MOLLUSCA. EOLIS. 7 



gymnota, COUTHOUY. Bost. Journ. Nat. Hist., ii. 69, 

 pi. 1, f. 3. Nearly an inch long, slender, whitish ; tentacula four, 

 the inferior pair smooth and round, the superior rather shorter, 

 compressed and minutely serrated at their sides ; branchial ap- 

 pendages reddish- brown, disposed in seven remote clusters of five 

 each, along each side of the back, those of the second and third 

 pairs longest ; back otherwise naked. 



There are also a few animals whose organization brings them 

 into a different class (Annelida), which form for themselves a solid 

 covering. As they are usually included in systems of Concholo- 

 gy, it may be well to introduce them here. 



These coverings are sometimes composed of clay, sometimes 

 of agglutinated particles of sand, and some are calcareous secre- 

 tions, like the usual material of shells. They are all of a tubular 

 form, tapering posteriorly, and hence the animals which construct 

 them are called Tubicola. 



PECTINA'RIA Belgica, LAM. (Jlmphitrite auncoma, MULL.), 

 State Coll., No. 266, has a conical tube, a little curved, about two 

 inches long, and a fourth of an inch in diameter at the larger end. 

 It is composed entirely of grains of sand, cemented together by a 

 glutinous secretion of the animal, in a single layer, and in regular 

 order. Of course the tube is very fragile. The animal appears at 

 its aperture, bearing on its head two tufts of short, golden plumes. 



It is not unfrequently found thrown upon the sandy shores of 

 Cape Cod and the neighbouring islands. (FIGURE 1.) 



From the stomachs of fishes I have taken specimens of Pecti- 

 naria which may belong to a different species. They are com- 

 posed of very fine grains of sand, are not easily crushed, not 

 more than an inch in length, and quite as much curved as the 

 horns of cattle usually are. State Coll., No. 270. (FIGURE 2.) 



AMPHITRI'TE ventilabrum, LAM. (Sabella penicillus, LIN.), 

 State Coll., No. 259, has a long tube, more or less contorted, com- 

 posed of clay. The animal, when protruded, exhibits two beautiful 

 tufts of long> finely feathered branchiae. It is very common on the 

 under side of logs which have lain for some time in the timber- 



