and Species of Nudibranchtate Mollusca. 141 



In the diagnosis of the genus given by Adams and Reeve* 

 the dorsal tentacles arc said to be non-retractile — a statement 

 repeated in Brunu's 'Thiern'ich 't) 'dthough corrected in Alder 

 and Hancock's ' Synopsis '|. They are certainly retractile in 

 the tuur species represented in the British-Museum collection. 



The following species of Ceratosoma have been hitherto 

 figured: — C corniyerum^ xVd. & Reeve § {== Dun's trijida^ 

 Gray), C. trilobatum, Gray, a.nd C. graciUimum, Semper ||. 

 The first alone has been described. 



Ceratosoma tenue^ sp. nov. PI. VII. figs. 5, 5 a, b. 



C. triungulare, prisiuaticum, latcraliter compressum, molle ; dorso 

 piano, leviler trilobate; turaore postbranchiaU eomplanato ligu- 

 lato ; colore fidvesceuti-Iactco, punctulis pallidioribus maculato, 

 et lineis reticulatis remisse notato ; tentaculis dorsalibus brevibus 

 clavatis, ad apices rotuudatis, minute lamiuatis, in foramina an- 

 gusta profundacjue retractilibus ; branchiis magnis graciUbus ante 

 tubulatura anura, e tribus radicibus orient ibus, in foramen retracti- 

 libus; ore utriusque parva depressione pracdito, pede lineali usque 

 finem longaecaudte extenso, margine antice lobulato etintlecto. 



The body is prismatic, and is triangular in lateral outline, 

 raised in the central branchial region, smooth and soft. The 

 mantle is obsolete. The dorsal surface is flat or gently curved, 

 and a little constricted behind the dorsal tentacles ; it gradually 

 rises from above the mouth, and culminates behind the branchiae 

 in a flattened, ligulate, roundedly pointed fleshy appendage. 

 Beneath the latter the body falls abruptly, and then curves off 

 into the laterally compressed, elongated tapering tail, which 

 occupies about four tenths of the total length of the animal. The 

 thickened and slightly overhanging border of the supracapital 

 surface is marked by a rather thick semitransparent line lying 

 between two opaque irregular ones. Two pairs of short, 

 curved, similarly bordered lines are found upon the sides of the 

 dorsal surface, and a somewhat similar marking margins the 

 postbranchial protuberance. The dorsal tentacles are short, 

 clavate, rounded at the apex, and minutely and diagonally 

 laminated ; they are retractile within deep narrow cavities, 

 which have the border slightly protuberant. The branchife, 

 about twenty-one in number, are long and slender, and arise 



• ' Zoology of the Voyage of II.M.S. Samarang,' Mollusca, pp. G7 & 

 68, pi. xix. f" o. 



t ' Thierrt- ich,' Band iii. p. 798. 



J ' Monograph of the British Nudibranchiate Mollusca,' Appendix, 

 p. xix. 



§ Loc. cii. 



|l 'Reisen im Archipel der Thilippinen,' Theil -, liiud ii. Heft 5, t, 25. 

 f. 8. 



