and Species of Nudthranchiaie Molhisca. 145 



Trevelyana concinna^ sp. nov. PI. VII. figs. 8, 8 a, 8 h. 



T. laevis, in regione brauchiali levata, dilatataque, pallio distincte 

 caren8,unicolorata ; tentaculis dorsalibus parvis rotundatis, minute 

 laminatis, confertis, retractilibus ; branchiis sexdecem, arrectis, bi- 

 piunatis, non-retractilibus, medialiter in dorso, ante et partira 

 cireum anum positis ; pede ad fineni caudae extenso, antice cum 

 fossa transversali cujus lamina anterior lata est, et in duos lobos 

 laeves rotundatosque medialiter divisa. 



The body is elongate, somewhat compressed laterally, convex 

 above, the central branchial region being the highest, smooth. 

 There is no indication of a mantle, nor any appendages. The 

 dorsal tentacles are short, rounded and nodular, finely marked 

 with rather upright laminae, and retractile in cavities which 

 are placed close together on the head. The branchiee, fourteen 

 to sixteen, are upright, bipinnate, non-retractile, set on the 

 centre of the back at a little distance from and around the 

 anus, in an arc occupying three fourths of a circle, the con- 

 vexity being forwards. The integument is gently raised out- 

 side the plumes. The mouth is terminal, without oral tentacles, 

 but their position is indicated by two indistinct slightly raised 

 oval surfaces placed superiorly to the opening. The foot is 

 linear, truncate in front, and extends behind to the end of the 

 tail, where it terminates in a point ; in front tliere is a deep 

 transverse groove, the anterior lamina of which is wide antero- 

 posteriorly, and divided by a median depression into two, flat, 

 rounded lobes ; the border of the foot is rather thickened and 

 free. The colour of the spirit specimen is a light semitrans- 

 parent brown, with the tentacles, the branchiae, and the foot 

 opaque. 



The length in spirit is 30 millims., the breadth 10, the 

 height 12. 



The specimens were obtained in the Gulf of Suez. 



T. concinna appears to differ from T. ceylonica principally 

 in the absence of markings, from T. impudica in the absence 

 of dorsal tubercles, and from the other species in the shorter 

 and less depressed body. 



EXPLANATION OF THE PLATES. 

 Plate VI. 



Fig. L Calycidoris Giintheri, upper surface. 1 a. Branchiae, enlarged. 



1 b. Under surface. 1 c. Side view. 

 Fig. 2. Hexabranchtis pellucididus, side view. 2 a. Upper surface. 2 h. 



Another specimen, side view. 2 c. Under surface. 

 Fig. 3. Hexabranchus suezensis, half nat. size, seen from above. 3 a. Seen 



from below. 

 Fig. 4. Plocamopherus nrpvahts. 4 a. Under surface. 



