68 TETHYS. 
Section Neaplysia Cooper, 1863. 
Swimming lobes short, somewhat united behind ; opaline gland 
opening externally by a single orifice ; mantle having a minute sub- 
central tube communicating with shell cavity; shell having a mem- 
branous erect accessory plate arising near the apex. Type and only 
species, 7. californica Coop. 
Section Aplysia Linné, 1766. 
Swimming lobes ample, united behind the excurrent siphon ; opa- 
line gland multiple, opening externally by numerous independent 
ducts; mantle having a rather large oval thin-edged opening into 
shell cavity ; shell with no accessory plate, usually convex and cal- 
eareous. Type, 7. depilans Linné. 
Subgenus PHycopHiLa Adams, 1861. 
Body compressed with long tail and narrow sole. Type, T. 
euchlora Ad. 
In the following pages the species are arranged geographically, 
this being, perhaps, the best plan for the present, many forms being 
still known by the shell alone, and the characters necessary for the 
natural classification of some others are still unknown. 
The section Neaplysia consists of but one known species, NV. cali- 
fornica, p. 89. 
Section Aplysia is widely distributed, and contains the following 
species : 
European Seas: punctata, depilans. 
West Atlantic and Antillean: parvula. 
West America: rangiana, (? nigra, ? inea). 
Polynesia : elongata. 
Australian Seas: concava ? 
China and Japan: fusca. 
Western Indian Ocean: nigrocineta. 
Habitat unknown. anguilla ? 
Section Tethys is the most numerous in species, and occurs on all 
tropical and warm temperate coasts except western North America. 
All species not enumerated above are supposed to belong to this 
group; and probably nigra and inca of Orbigny also group here, 
although they have the swimming lobes united behind as in the re- 
stricted section Aplysia. 
