sponge-fauna vf Norway. 451 



Leptochrota — the similarity in names, however, being only 

 what we call accidental, arising really from our both having 

 the same idea to express in a single word. Thomson's sub- 

 order, however, was intended to include monaxonid as well 

 as tetractinellid sponges, and thus, ignoring a distinction 

 which all spongologists are now agreed to regard as funda- 

 mental, cannot be maintained. This is not the case with 

 Leptochrota, which is a division of the Tetractinellida3, not of 

 the heterogeneous group Radiantia ; Leptochrota, therefore, 

 escapes anticipation, though by a very narrow chance. 



As secondary characters distinguishing Thenea we may 

 cite the vesicular character of the canal-system, the super- 

 abundance of clear gelatinous matrix in the mesoderm, and 

 the substitution of spinipirules for stellates. As agreements 

 of doubtful value with other sponges, we have the similarity 

 in size of its flagellated chambers with those of the Corticata 

 and such Esperke as I have examined, and the resemblance 

 of its club-shaped spicules to those of the Esperiad R. Mar- 

 shall-HalU. This latter resemblance I regard as possibly 

 due to homoplasy ; but in any case it is eminently suggestive 

 of the manner in which the tetractinellid spicules have been 

 evolved. 



Distribution. — Kors Fiord, Norway. Station 13, 200 to 

 300 fathoms. The following occurrences are also recorded : — 

 Atlantic, 58° 23' N., 48° 50' W.; 1913 fms. ( Wright). Loc.'i 

 500 fms. [Kent) ; Florida, 178 frns. {0. 8.) ; between Anti- 

 costi and Gaspe, 220 fms. {Whiteaves) . Grey ooze gene- 

 rally (IF. Th.). 



Broadly speaking, therefore, it is known on both sides of 

 the Atlantic, from Norway to Florida, and ranging from 100 

 to 2000 fathoms in depth. Probably its area will be found to 

 be much more extended than this : there is, indeed, a sugges- 

 tion of its occurring in the Pacific ; for Mr. Norman has placed 

 in my hands a specimen which seems specifically identical 

 with T. Walh'chii, and which came, according to the assertion 

 of the dealer who sold it, from Cebu. 



EXPLANATION OF PLATE XVII. 

 Thenea Wallichii, P. Wright. 



Fig. 1. One of the coarsely granular cells in the connective tissue sur- 

 rounding a sperm-ball ( X oOO). 



Fig. 2. Median longitudinal section through the sponge: o, the osculo ; 

 t, tegminal edge ; e, equatorial recess (nat. size). 



Fig. 3. A variety of acerate spicule, with swollen distal end (probably a 

 precursor of the tetractinellid form) (X 30). 



