144 HEXACTINELLA MONTICULARIS. 



and discohexasters or oxyhexasters or tylehexasters or two of these forms. With- 

 out microonychhexactines and tylostyles with slender branch-rays, bearing end- 

 discs, on the tyle. 



The collection contains one specimen and three fragments of this genus. 

 The specimen is insufficiently preserved for specific distinction. The three 

 fragments all belong to a new species. 



Hexactinella monticularis, sp. nov. 

 Plate 28, figs. 1-28. 



Three fragments of the skeleton of this sponge were trawled south of Chat- 

 ham Island, Galapagos, at Station 4642 on 7 November, 1904; 1° 30.5' S., 89° 

 35' W. ; depth 549 m. (300 f.); they grew on broken Globigerina shells; the 

 bottom-temperature was 48.6°. 



From the surface broad and truncate conic protuberances arise and to these 

 the name refers. 



Shape and size. The three fragments measure 16, 17, and 20 mm. in maxi- 

 mum diameter respectively. All appear to be parts of an irregular massive 

 sponge with stout, truncate, conic protuberances. One of these protuberances, 

 which is about 4 mm. high and 8 mm. broad at the base, is represented (Plate 

 28, figs. 23, 28). 



The colour in spirit is brown. 



The skeleton consists of an internal and superficial network and loose hexac- 

 tines, pentactines, uncinates, discohexasters, and scopules. 



The internal skeleton-net (Plate 28, figs. 23, 24, 26, 28) forms meandric 

 lamellae, mostly nearly 0.5 mm. thick, which appear as the walls of tubes, with 

 lumina more or less circular in transverse section and about 1 mm. wide. In the 

 interior of the sponge these tubes are variously curved and irregular in their 

 course. On ajjproaching the surface they straighten out. On the whole they 

 extend chiefly radially and longitudinally from the base to the upper and lateral 

 parts of the surface, where they open out. The openings are fairly equidistant 

 and uniformly distributed, as numerous on the summits and the sides of the 

 monticular processes as on the other parts of the surface. Since most of the 

 tubes reach the surface obliquely their superficial openings are more or less oval 

 (Plate 28, figs. 23, 28). It is to be presumed that the tubes form two systems, 

 one afferent, vestibular ("Epirhysen"); the other efferent, preoscular ("Apo- 

 rhysen"). 



