35 



Triopa incisa, M, Sars, 



n. sp. 

 (PI. III. fig. 1-3). 



Of this remarkable Xudibranch I have only observed some few specimens all taken 

 from great depths at Lofoten. It varies in some respects so considerably from the 2 other 

 known species of the genus, that it ought perhaps more properly to be considered as the 

 type of a particular genus. However I note it here preliminarily under the denomination 

 assigned to it by my Father; because, owing to the scarcity of specimens, I have not been 

 able to institute an investigation in minute detail. 



The animal is only 7 Mm. in length, that is considerably less than our other two 

 species, but yet appears to be full grown. The shape is rather short and plump, with a high 

 convex dorsal side; seen from above (fig. 1.) oblong oval, in front obtusely rounded, both the 

 side edges only a little curved, or nearly parallel, and the posterior extremity suddenly much 

 narrower and conically pointed. 



The mantle is particularly large and wide, and in the upper part strongly convex, 

 advancing far beyond the foot in front, as also it extends beyond the foot on each side to 

 about l / 4 of its own breadth, in the form of a sharp and thin border (see fig. 3). At the 

 commencement of the posterior third part of the length of the body the mantle terminates, 

 shewing at this part a crescent-formed incision, or going out into 2 triangularly pointed lobes 

 that project on each side of the conically tapered posterior part of the body. From the 

 anterior extremity of the mantle there proceeds upwards in the middle (see fig. 1 & 2) a 

 tolerably high longitudinal keel, which however is quite short, and soon becomes forked into 

 2 somewhat diverging branches which surround an oblong triangular area in the middle of 

 the dorsal side. These diverging keels, which like the single keel are thin and vertical, are 

 somewhat irregularly lobed, and were in one specimen resolved into several separate pro- 

 cesses; somewhat behind the middle of the animal, each of them terminates in an obtusely 

 conical lobe or process directed backwards and somewhat outwards. On each side of these 

 diverging longitudinal keels, between them and the edge of the mantle, there is a longitudinal 

 row of 4 G short cylindrical obtusely terminating processes. 4 similar but larger processes 

 are situated further in front, namely 2 quite close together near to the anterior edge (one 

 on each side of the single medial keel) and 2 further from each other somewhat larger near 

 to the side edges of the mantle and by the exterior side of the dorsal tentacles. Finally 

 there is, at the posterior extremity of the area in the middle of the back above-mentioned, 

 a transverse row of 5 processes, of which the middle and the two extreme ones are very 

 strongly elongated, smaller at the base, and somewhat enlarged at the extremity, or elongated- 

 claviform, while the 2 others are very small and of the same shape as those in the lateral 

 rows. All these 5 processes are directed obliquely backwards and upwards, and the mantle 



