38 THE VOYAGE OF H.M.S. CHALLENGER. 



more numerous, but measuring in length only about 0"12 mm. The ends of the pedicels 

 and tentacles have a number of straight or slightly curved, more or less spinose spicula. 



Tabular View of Species of the Genus Scotoplanes. 



I. Pedicels all along each side of the ventral surface. 



A. Body elongated, posteriorly extremely depressed with the flat truncated posterior 



end deeply incised in its middle. Calcareous deposits : C-shaped spicula and 



three-armed bodies, ....... . Scotoplanes insignls. 



B. Body more or less elongatedly ovate or almost globular. Calcareous deposits : 



C-shaped spicula, and large, straight, unbranched ones. 



a. Perisoma brittle and glassy, . .... Scotoplanes mwirayi. 



b. Perisoma thin, soft, and pliable. 



1. Pedicels seven along each side of the ventral surface. Dorsal surface, 



with three pairs of processes, the two first pairs being very large 



and elongatedly conical, ...... Scotoplanes globosa. 



2. Pedicels six along each side of the dorsal surface. Dorsal surface, 



with two very large elongatedly conical processes side by side near 

 its middle, and with two smaller ones issuing one from the outer 

 side of each of the former, ..... Scotoplanes mollis. 



3. Pedicels eight along each side of the ventral surface. Dorsal surface, 



with a low transverse ridge near the middle, bearing four very small 



processes, and witli two rudimentary processes behind this ridge, . Scotoplanes papillosa. 



4. Pedicels ten or eleven along each side of the ventral surface. 



Dorsal surface, with some small processes anteriorly, . . Scotoplanes albida. 



II. Pedicels only around the posterior half of the ventral surface. Calcareous deposits : 



C-shaped spicula and three-armed bodies, ...... Scotoplanes robusta. 



Irpa, Danielssen and Koren. 

 Irpa, Dan. and Ivor., Nyt Magazin for Naturvidenskaberne, xxiv. 3, 1877. 



Irpa ahyssicola, Danielssen and Koren. 



Body elongated, nearly cylindrical, about thrice and a half as long as broad. Mouth 

 anterior, almost terminal. Anus posterior, terminal subdorsal. Tentacles of almost equal 

 size ; their terminal part, with small digitate processes. Pedicels cylindrical, twelve 

 along each side of the ventral surface. The dorsal surface, only in its anterior third, 

 with two anteriorly diverging rows of processes, four in each, and with two slightly 

 larger processes between the two rows. Integument leathery, with two sorts of 

 calcareous deposits : scattered small, straight or curved horseshoe-shaped spinose 

 spicula, rarely provided with some branches ; and numerous very small elliptical bodies. 



Length, about 21 mm. Breadth, about 6 mm. 



Habitat.— Station 35. Lat. 63° 22' N., long. 1° 20' W. Depth, 1050 fathoms; 

 bottom temperature, l - 3° C. ; grey-brown mud. One specimen dredged by the 

 Norwegian North Atlantic Expedition. 



