Revision of the Genus Lomanotus. 205 



XX. — Contributions towards a Revision of the Genus 

 Lomanotus. By Nathaniel Colgan, M.R.I. A. 



While dredging off Bullock Harbour, Dublin Bay, on the 

 6tii October, 1906, what seemed to be a fairly successful haul 

 was made in 10 fathoms low water. As there was a heavy 

 rolling sea on, and our small boat was much too lively to 

 permit of any careful sorting of tlie contents of the dredge, 

 the whole haul was emptied into a bucket of sea-water. On 

 landing soon after I observed floating near the surface of the 

 water in the bucket a prettily frilled, rosy orange-coloured 

 animal quite unfamiliar to me, yet obviously a nudibranch. 

 It was transferred to fresh sea- water in a glass jar, when it 

 immediately began to swim vigorously to and fro and up and 

 down, with a rapid, lashing, serpentine motion of its flexible 

 body, the thin foot-margins being drawn inwards and down- 

 wards so as to form a sharp keel favourable to quick and 

 graceful navigation. For a nudibranch it had a singularly 

 dashing manner. It darted rather than swam, as if it gave 

 way to fits of petulance whenever it found its motion impeded 

 by the translucent yet impenetrable walls of its prison. The 

 animal lived in captivity for a day and a half, so that I had 

 ample opportunity of observing it and drawing up the 

 following tolerably minute description : — • 



Length of living animal fully extended 1| inch. General 

 colour of upper surface translucent rosy orange, of the sides 

 paler, passing into whitish on the under surface, no distinct 

 colour spots or blotches being apparent anywhere. Body 

 elliptic-oblong, deep (not flat), gradually narrowed behind 

 into a very short and ill-defined tail. Foot with two slender 

 tentacular processes on each side in front, the anterior pair 

 usually carried in a recurved or hooked posture. Dorsal 

 tentacles or rhinophores two, bright yellow, club-shaped, 

 obliquely laminated, suddenly narrowed above into short, 

 blunt, cylindric-conic, smooth, white tips and rapidly retractile 

 within long sheaths. Margin of the right-hand sheath (as 

 one looks towards the head of the animal) divided into 4 (or 

 5 ?) irregular teeth or lobes, that of the shorter, left-hand 

 sheath, simple or at most sinuate. Along each side of the 

 back runs an erect, flexible, frilled process, the pleui'opodium 

 or pallial margin {Ruckengehrdme oi Bergh), waved into three 

 deep bays whose convexity points inwards towards the median 

 line of the animal. The upper margin of this frill is cut into 

 not very numerous tooth-like, flattish, triangular segments 

 (branchial papillte?) of unequal size, the longest occupying 



