46 



April 2, 1851. 

 Dr. Samuel Cabot in the Chair. 



Mr. W. O. Ayres made a communication with reference 

 to the Holothurian recently described by Mr. William 

 Stimpson, as Anapcrus wiiscmita. 



From the examination of that specimen, which belonged to 

 the Society, and another in much better condition, belonging to 

 the Essex County Natural History Society, he was convinced 

 that the species was not an Anaperus, but the type of a new 

 genus. 



The peculiar character of the integuments, indurated with 

 calcareous deposits, suggests a generic name, and it may be 

 called 



STEREO DERMA. 



Body ovate-elongate, with both extremities slightly elevated, 

 thus distinguishing a superior and inferior side ; the entire sur- 

 face covered with minute, perforated, calcareous plates, so 

 thickly as to render the walls of the body rigid and hard ; ten- 

 tacula ten, (of which two on the ventral side are much less than 

 the others) stiff and unyielding, somewhat ramose ; oral circle, 

 like that of Psolus, consisting of ten pieces, tapering anteriorly ; 

 retractor muscles very long and slender ; suckers scattered 

 irregularly over the body, excepting beneath where they form a 

 well-defined line ; respiratory trees not largely developed ; geni- 

 tal tubes undivided ; stomach muscular. 



The genus is allied to Sclerodactyla by the structure of the 

 tentacula, and to the same genus as well as Sporadipus, Aiiape- 

 rus^ and Orada, by the arrangement of the suckers, (though dif- 

 fering from them all in the line beneath,) but distinctly charac- 

 terized by the hard integuments, and by the other features 

 already noted. 



Of its geographical range little is known. The specimen here 

 descrihed was brought from the Banks of Newfoundland ; the 

 one in the Society's Collection was probably taken on the coast 

 of Massachusetts. It is a small species, not much exceeding two 



