No. 19.] ECHINODEEMS OF CONNECTICUT. I3S 



The calcareous ring at the base of the tentacles is very broad, 

 and the radial plates have rather slender prolongations. 



The internal anatomy of this species is described in detail on 

 pages 116 to 122, and is illustrated on Plate XXX. The habits 

 and reactions to stimuli have recently been studied by Pearse, and 

 are described in an interesting article in the Biological Bulletin, 

 Vol. XV, pp. 259-288, 1908. The sexual products mature in June. 



Thyone unisemita (Stimpson) 

 Single-striped Thyone 

 Plate XXXII, fig. I. 



In the earlier writings of Ayres and Verrill this species was 

 placed in the genus Stereoderma, and as such appears in Verrill 

 and Smith's Invertebrate Animals of Vineyard Sound. There 

 are few available records of the collection of this species in Long 

 Island Sound. The United States Fish Commission collected 

 twelve specimens off Watch Hill, Rhode Island, at a depth of 

 eleven fathoms. Six of these specimens are preserved in the 

 Yale University Museum. The Fish Commission likewise records 

 the collection of two other specimens in Long Island Sound, but 

 without giving the number of station or precise locality. The 

 species has also been dredged on sandy bottoms at various local- 

 ities from southern New England northward to the Banks of 

 Newfoundland, but has nowhere been found in abundance. 



The living animals are white, flesh-colored, or yellowish white, 

 with orange-yellow tentacles. Most specimens are less than two 

 inches in length, although one individual measuring three inches 

 in length has been recorded. 



The body is somewhat U-shaped, and narrowed at both ends. 

 The pedicels cover the dorsal and lateral surfaces, but on the 

 ventral side there is only one double row situated along the mid- 

 ventral line. This row is rendered the more conspicuous because 

 it is bordered on each side by a wide area of smooth skin, giving 

 the characteristic effect of a single ventral stripe. 



The calcareous deposits in the body wall (Fig. 26) consist 

 of flattened plates, many of which are symmetrical and perforated 

 by four holes. Others are larger, irregular in outline, and with 



