/ 78 NEW GENERA OF MONAXONID SPONGES, 



vided : the largest observed spicule with spinules measured 475 

 x 12/k. 



(iii.) The dermal spicules (Text fig. 1, c) are slightly to 

 moderately curved subtylostyli, with somewhat fusiform shaft, 

 and invariably provided with a cap of spinules on the basal 

 extremity. Those located actually in the dermal skeleton range 

 from about 100 up to 165//, in length and up to 7.5//. in stout- 

 ness; but spicules of similar form, occurring scattered between 

 the skeletal fibres, range in size up to occasionally as much as 

 240 x 10//.. In their earliest developmental stages the dermal 

 spicules are extremely slender tylostyli, the smallest of which 

 are only about 80/x in length. 



Microscleres.- — (i.) The larger isochelae palmatae (Text-fig 

 1 d,) are of the ordinary type occurring in Clathria and related 

 genera, and measure from 14 to 22//. in length. 



(ii.) The smaller isochelae palmatae (Text-fig 1, e), like those 

 of Rhaphidophlus typicus Carter, are peculiar in being fre- 

 quently asymmetrical with respect to their opposite extremities, 

 ■ — the asymmetry "being such as would result through tor- 

 sional rotation of one end of the shaft through an angle 

 of 90° . They appear often to be somewhat abnormal in other 

 respects also, but the details of their form are difficult to 

 make out owing to their very minute size. They measure only 

 from 4 to 8//. in length. 



(iii.) The toxa (Text-fig. 1, /, /', ) comprise an apparently 

 complete series of forms, of gradually varying shape, ranging 

 in length from less than 10//. up to occasionally as much as 800 //. 

 The shortest and by far the most numerous, — seldom much ex- 

 ceeding 80 or 90//, in maximum length, — are more or less dis- 

 tinctly tricurvate; those of intermediate length have the arms 

 straight or nearly so, and are bent in the centre somewhat angu- 

 lately; and the longest are mostly quite straight, resembling ex- 

 tremely long and slender, rhaphidiform oxea. The last-men- 

 tioned, — although usually difficult to discover in sections of the 

 sponge owing to the multitude of other spicules, — are in some 

 specimens by no means rare; but in others they appear to be 

 almost entirely absent. In one of the latter specimens, the 

 longest rhaphidiform toxa that could be found measured only 

 360 x 2/x ; whereas in the specimen in which they were most 

 numerous, the longest one observed measured 810 x 4.5//.. 



Embryos. — Most of the specimens contain not very numerous, 



