REPORT ON THE CALCAREA. 59 



. [cerate spicules.— 01 three kinds. Large acerate spicules of the parenchyma. — Straight, probably 

 exceeding 25 mm. in length, with a diameter of 006 mm., projecting from outer surface. 

 They are extremely rare, and having always found them with the free end broken off, 

 I can give no more precise statements as to their length. Small acerate spicules of the 

 ■parenchyma. — Also rare, sparsely scattered here and there in the parenchyma near the 

 outer surface, either in small heaps or isolated, usually situated perpendicularly to the 

 surface, often showing no order in their disposition ; average size : 0-3 mm. by 00025 mm. 

 Linear acerate spicules of the 'peristome. — Fine, smooth, either straight or slightly curved, 

 sharp-pointed, reaching 3 mm. in length and O'OOo mm. in diameter, often still thinner. 



Colour. — Pale yellowish. 



Habitat. — Station 30, April 23, 1873; off Bermudas ; depth, 32 fathoms; mud. 



Leuconia levis, n. sp. (PI. VII. figs, ia-id). 



The two specimens of the Challenger collection for which I establish this new species 

 present elongated thin-walled tubes almost of the same diameter throughout their whole 

 length, and only growing narrower close to the lower end like a wedge. The larger 

 specimen is 50 mm . long, 7 mm. thick; the thickness of the walls is about - 75 mm. 

 The outer surface is smooth, the inner slightly roughened by the apical rays of the 

 gastric quadriradiate spicules. The chief character of the species consists in the slender- 

 ness of its spicules. This is also common to Leuconia Jistulosa, Bk., and Leuconia 

 pumila, Bk., yet the size of the spicules, their form and their disposition, distinguish 

 Leuconia levis from Leuconia pumila ; on the other hand, the absence of the acerate 

 spicules and the comparative shortness of the apical ray of the gastric quadriradiate spicules 

 do not allow us to unite this form with Leuconia Jistulosa, the rays of whose spicules 

 are still more slender. 



Skeleton. — The skeleton consists of gastric quadriradiate, of subgastric quadriradiate, 

 of parenchymal triradiate, and of dermal triradiate spicules. 



Gastric quadriradiate spicules. — All rays of the same average diameter of 0015 mm.; facial 

 rays cylindrical, either sharply or bluntly pointed, apical ray tapering from the base to a 

 sharp point; basal ray straight, forming with each lateral ray an angle of 118°, usually 

 twice as long as lateral rays, often still longer, not exceeding, however, - 45 mm.; occasion- 

 ally rather shorter; lateral rays either straight or slightly curved, often rather undulating, 

 their average size 0'175 mm.; apical ray curved, rarely longer than 009 mm. 



Subgastric quadriradiate spicules (lateral and apical rays in the plane of the gastric surface, 

 basal ray directed centrifugally).- — All rays smooth, tapering from the base to sharp points ; 

 facial rays of the same average diameter (0 - 0125 mm.) ; apical ray rather thinner ; basal 

 ray straight, usually 0-3 mm. long, forming with each of lateral rays an angle varying 



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