758 ME. A. G. THACKER ON [June 16, 



Leucosolenia tenuipilosa Dencly) have been supposed to be speci- 

 fically distinguished from Haeckel's original Ascaltis canariensis 

 ^re i-eally quite inconstant and not of specific value. As used by 

 me, therefore, the name Leucosolenia canariensis includes sponges 

 which have been hitherto considered to be specifically distinct 

 fiom each other, and in my description of this species I have 

 endeavoured to give a detailed justification of this procedure. 



The calcisponge fauna of the Cape Yerde Islands shows distinct 

 aftinity with that of the western side of the Atlantic. In a 

 letter to Professor Minchin, Mr. Crossland suggested that the 

 distribution of these species might prove interesting because the 

 Islands receive currents from the Gulf Stream. This forecast has 

 been to some extent corroborated, iov Zeiocosolenia panis has been 

 i-ecorded from the coast of Florida (immediately in the course of 

 the Gulf Stream, of course), and Leucandra tyjyica and Leucandra 

 rudifera w^ere dredged by the ' Challenger ' off Bermuda (also not 

 far from the Gulf Stream) on the same day and from the same 

 spot. I think, therefore, that it is not impossible that the Gvilf 

 Stream may be a factor in the distribution of all three species ; 

 but it should not be forgotten that the North Equatorial Current, 

 which takes its origin near the Cape Yerde Islands and meets the 

 Gulf Stream as the latter issues from the Gulf of Mexico, might 

 produce precisely the same results by distributing the sponges in 

 the opposite direction, that is, by carrying them westwards instead 

 of eastwards. The distribution of Leucandra typica may not be 

 of much value in estimating these factors of dispersal, because 

 having been recorded from Australia it is evidently a widely 

 distributed if somewhat uncommon species, but in the case of 

 L. panis and of L. rudifera, each of which has only been found 

 once before, the facts here stated are of greater significance. Leu- 

 candra sericata is a sponge inhabiting the Atlantic coast of South- 

 America. Of the remaining two species which are not new, 

 Z. canariensis has a very wide range and Sycon quadrangtdatum 

 has been recorded from the Arctic, from the eastern Atlantic, and 

 from the Mediterranean. 



Where it has been'^'iiecessary in the following pages to refer to 

 individual specimens, I have done so by the use of the Registered 

 Number {^R.J}^.) which I have attached to each specimen in the 

 collection*. The numbers in square brackets — thus [1] — refer to 

 the works given in the list of literature at the end. The list only 

 includes such memoirs as I have had to refer to in the text. 



Throughout this paper I have followed the classification of the 

 Calcarea, set forth by Dendy in [9] and [11]. According to this 

 system the genera Leucosolenia and Leucandra are very com- 

 prehensive, the former including all the Homocoela and the latter 

 being extended to inckide species such as my L. verdensis, which 



* The collection lias been placed in the University Museum of Zoolog}^ at 

 Cambridge. 



