4 INVERTEBRATA OF MASSACHUSETTS. 



It is found in rich grounds under stones and pieces of wood, 

 where it may be sheltered from the sun ; and I do not recollect 

 ever to have found one except in company of what are vulgarly 

 called sow-bugs (Porcellio). It is a true Limax, and may be the 

 L. agrestis of Europe. 



The aquatic species are much more numerous, and are found 

 in every sea. They are all remarkable for the peculiar arrange- 

 ment of their branchiae or respiratory organs. These are ex- 

 posed on the exterior of the body (Nudibranchiatd) Cuv.) in the 

 form of little tubercles, filaments, plumy tufts, or branched leafets ; 

 and the great diversity of their shape, arrangement, and coloring, 

 constitutes the principal ornaments and most obvious character- 

 istics of the animals. They have four tentacula or feelers, two 

 of which are in the neighbourhood of the mouth, and are not con- 

 spicuous, and the other two placed at some distance behind the 

 head, capable of being withdrawn out of sight, and presenting a 

 laminated structure when extended. They crawl upon the bottom 

 of the sea, or the roots of marine plants on which they feed. 

 They are arranged under different genera according to the dis- 

 position of their branchiae and tentacula. 



In DORIS, the branchiae have an arborescent appearance, are 

 capable of being retracted, are seated on the middle line of the 

 back behind the centre, and are arranged about the anal orifice in 

 a circular manner (Cyclobranchiata, Blainv.). But one species 

 has as yet been observed, and of this I have been unable to find 

 any description. I have, therefore, ventured to describe it under 

 the name of 



DORIS illuminata. Animal prismatic, somewhat four-sided, 

 the back arched ; color a pearly white, or light dove-color, dotted 

 with greenish ; front of the foot slightly dilated at angles ; upper 

 lip full and strongly pursed ; a line of six tubercles on each side 

 diverges from the front to each side of the tentacula, making the 

 back, at this part, of a four-sided form ; between these and the 

 branchial tuft are four more tubercles on each side, in parallel lines, 

 and then follow two on each side much longer than the rest, of a 

 somewhat club-shaped form, followed by a few smaller ones to- 

 wards the tail ; sides and back dotted by several small tubercles ; 



