102 



numerous living specimens of Sclerodactyla briar eus had 

 shown some points of interest in regard to both the habits 

 and structure of the species. 



It is found on muddy bottoms, from low water mark to three 

 or four fathoms. It lies commonly among the roots of the 

 Zostera, just beneath the surface of the mud, with the two 

 extremities protruding above. Its motions are very sluggish, 

 an occasional slow vi^aving of a tentacle and the opening and 

 closing of the anus for respiration being the only signs of life 

 visible often for many minutes. The form of the body also 

 changes very gradually by contractions of the transverse mus- 

 cles. The process of respiration is curious and interesting. 

 The sides of the posterior portion of the body are seen to flatten, 

 from the contraction of the slips joining the walls to the cloaca ; 

 the anus is expanded and remains so for two or three seconds 

 during which a current of water is constantly entering. This 

 operation is repeated three or four times at intervals of twenty to 

 thirty seconds, and then the whole is expelled at one effort with 

 considerable force. In shallow water the extremity is often 

 raised above the surface for expiration, and the ejected column 

 is thrown to the height of three or four inches. Where a num- 

 ber of specimens are kept in a basin, these miniature fountains 

 keep the water in continual agitation. 



Two points of structure were also detected, showing an entire 

 analogy with other species. 



The solid calcareous tubes supporting the tentacula were seen 

 under pressure to consist of very numerous, minute, elongated, 

 perforated plates. In some specimens the deposite was so far 

 deficient as scarcely to constitute a perfect tube, and here the 

 plates were readily seen. 



The oral circle was formerly described as consisting of a 

 single piece. This is strictly true, but an examination of this 

 organ in many specimens, when removed and dried, showed 

 that the single piece is formed by the union of the typical num- 

 ber, (ten,) as occurring in other species. Five of these are bifur- 

 cated anteriorly, (and to these, as usual, the retractor muscles 

 are attached,) and prolonged posteriorly in two slender points. 

 The remaining five are the representatives of those pieces in 



