REPORT ON THE MONAXONIDA. 221 



Locality.— Station 299, December 14, 1875 ; lat. 33° 31' S., long. 74° 43' W.; west 

 of Valparaiso; depth, 2160 fathoms; bottom, blue mud; bottom temjjerature, 35° '2. 

 Two specimens. 



Genus Tentorium, Vosmaer. 



1870. Tliecophora, Schmidt, Spong. Atlant. Gobiet., p. 50. 



1885. Tentorium, Vosmaer, Bronn's Klass. v.. Ordn. d. Thierreichs, Porifera, p. 329. 



Sponge sessile, columnar or conical ; protected by a dense, cylindrical sheath of 

 longitudinally placed spicules, which form a solid, imperforate layer. Over the top there is 

 a proper fibrous cortex containing bundles of smaller spicules arranged vertically to the 

 surface, between which are situate the large, elongated subdermal cavities. Pores on the 

 upper surface only. Oscula tubular, in the centre of the upper surface ; commonly only 

 one. Spicules tylostylote or subtylostylote. 



Schmidt gives no generic diagnosis, but Vosmaer, in addition to pointing out that 

 the name Thecophora is already occupied, gives the following: — " Cylindrischer mit 

 breiter Basis angewachsener Korper. Oben sind kleiue papillenartige Oscula. Riude 

 besonders deutlich oben. Spic. indie. tr° ox;, f. von verschiedener Grosse." 



Only a single species of the genus is as yet established. 



Tentorium semisuherites, Schmidt, sp. 



1870. TlieeoiJlwra semisuherites, Schmidt, Spong. Atlant. Gebiet., p. 50, pi. vi. fig. 2. . 



1873. Thecophora ihla, Wyville Thomson, Depths of the Sea, p. 147, fig. 24. 



1877. Thecophora elongata, von Marenzeller, Die Cffilenterateu, Echinodermeu und Wiirmer 



der K. K. Osterreichisch-ungarischen Nordpol-Expedition, jj. 12, 



pi. ii. fig. 4. 

 1885. Tentorium semisuherites, Vosmaer, Bronn's Klass. u. Ordn. d. Thierreichs, Porifera, 



p. 329, pL ii. fig. 4; jjl. xxi. fig. 19. 



This very interesting and well-characterised sponge is represented in the collection by 

 a fine series of ten specimens from Station 49, and a single very fine specimen, attached 

 to a stone, from Station 50. There are also four specimens, much smaller than usual 

 and characterised by correspondingly smaller spicules, from Inaccessible Island, which 

 we propose to consider as belonging to a dwarf variety, although the possibility of their 

 being young forms must be borne in mind. Hansen ^ has already given Thecophora ihla 

 and Thecophora elongata as synonyms of the original Tentorium semisuherites and we are 

 quite prepared to follow him in this. The difference between the three forms depends 

 very largely on the degree of contraction of the specimen ; when the specimen is in an 

 expanded condition, the top appears evenly rounded, as in Schmidt's original figure and 



1 The Norwegian North-Atlantic Expedition, 1876-1878, Spongiadse, p. 8. 



