Fara. 47.] NATURAL HL^TOKY SOCIETY. 129 



semicircular ; tentacles two, dilated and obtusely pointed ; gills 

 dilated at the centre, and with the dark centres appearing like 

 rude crosses, whence the name ; about 7 principal ones on each 

 side and 8-10 intermediate, much smaller ones. L. ; W. . — 

 Mass. 



8. Embletonia, a. and H. 

 Animal slender ; tentacles two, simple ; head produced into a 

 flat lobe on each side ; gills simple, subcylindrical, in a single 

 row down each side of the back. 



1. Embletonia fascata, Gld. Animal terete, tapering to a short, 

 pointed tail ; head large, angles rounded, slightly notched in 

 front; the two tentacles short, linear, capable of corrugations; 

 gills club-shaped, arcuate, arranged in 5 or 6 tufts on each side ; 

 2 or 3 front tufts contain 8 each, and the others 2, very unequal 

 in size ; foot angles not dilated. Pale drab to slate color, more 

 or less dotted. L. 4 ; W. f . — Mass. On timbers. 



2. Embletonia remigata, Gld. Similar to the last, but larger, 

 lighter in color, and witli longer gills. Color uniforui pale yellow; 

 the gills wax-yellow dotted with greenish, and having a pale 

 olive centre. . L. 6 ; W. 1. — Mass. On sea weed. 



Family 47. ELYSIID/E. 

 Animal with no distinct breathing organs ; respiration per- 

 formed by the ciliated surface of the body. 



* Wing -like expansions along the sides of the body 1. Elysia. 



* No wing-like expansions 2. Limapontia. 



1. Elysia, Risso. 

 Animal elliptical, depressed, with wing-like lateral expansions ; 

 tentacles simple, with sessile eyes between them ; foot narrow. 



1. Elysia chlorotica, Ag. Body slender, tapering, with broad, 

 wing-like expansions which fold over the back and overlap while 

 the animal is crawling ; when expanded, as in swimming, the 

 animal has a leaf-like look ; head and neck distinct, with two 

 lanceolate, folded tentacles. Emerald green, finely dotted with 

 white and red dots. L. 25-40 ; W. when folded, i length, when 

 expanded, J length. — Mass., in brackish water. 



2. Elysia catuhis, Ag. (Fig. 26). Body ovate-lanceolate, with 

 the lateral expansions f its length, and not meeting when folded ; 

 head large, rounded, globose; tentacles two, short, blunt, broad ; 



