113 



taken is that of an elongated cylindrical sac, bent like a siphon ; 

 but it soon commences contracting violently at various points, 

 after the manner of the Holoihuricp^ and frequently destroys itself 

 by rupturing the integument near the middle of the body. It is 

 four inches in length, and two fifths of an inch in diameter. Its 

 color is blood red, and it is everywhere covered with prominent 

 fleshy papillce, between which are often distributed minute, wart- 

 like rugosities. A depressed line runs along the middle of the 

 ventral surface, throughout its length. The mouth, situated at 

 the anterior extremity, is slightly protractile, in the form of a 

 membranous cup or short tube, and is surrounded by three or 

 four narrow concentric rings. The papillae in the vicinity of the 

 mouth also show a tendency to circular arrangement, but further 

 than this there are no indications of annulation upon the surface of 

 the animal. On the ventral surface, near the anterior extremity, 

 two slight prominences, one on each side of the median line, 

 bear the slender flattened hooks, which arise from their muscular 

 sheaths, precisely as in Echiurus. The intestine terminates pos- 

 teriorly in an anal pouch or cloaca, and the branchial caeca empty 

 into this pouch, instead of into the intestine above it. In other 

 particulars the internal structure is much like that of Echiurus, 

 as described by Quatrefages,* except that, in my specimens, only 

 two generative sacs could be made out, which opened externallv 

 just behind the hook-pouches. 



For this animal I propose the generic name Ancistropus, with 

 the following character : — 



Corpus elongatum, utriculare, cylindricum, papillosum ; unci- 

 nis duobus anticis instructum. Proboscis nulla. Os simplex, ter- 

 minate, in tubulum membranaceum protractile. Anus in extremi- 

 late corporis caudali locatus. 



Thalassema Americanum, Stimpson. 



The body of this species is short and thick, cylindrical ante- 

 riorly, and globosely rounded behind. The color is blood red, but 

 becomes whitish posteriorly ; ten narrow, longitudinal, whitish 

 bands are conspicuous in the living animal, and the body is often 

 covered with minute white dots. The surface is nearly smooth, 



* Voy. en Sicile, ii., 226. 

 PROCEEPINQS B. S, N. H. VOL. V. 8 FEBRUARY, 1855. 



