BY E. F. KALLMANN. 423 



The dermal skeleton, on the other hand, is quite different from 

 that of R. gracilis and very closely resembles that of B. viminalis 

 as depicted by Pick (32, PI. iii., fig. 1). Externally to the fibres 

 and the spicules of the main skeleton is a soft-tissued dermal layer, 

 usually not less than 300 /x in thickness, and almost entirely free 

 from scattered spicules; and this layer, which is crossed by the 

 deeply-embedded long tylostyli which project beyond the surface, 

 gives support superficially to elegantly radiate projecting tufts of 

 auxiliary spicules. These tufts occur not only at the points of 

 emergence of the tylostyli, but also between them. 



Spicules. — (a) The principal megascleres are exclusively styli 

 and tylostyli, which are similar in form and about equal in stout- 

 ness to the corresponding spicules of R. gracilis, and, like them 

 (though to a less appreciable extent), exhibit some degree of dif- 

 ferentiation into two groups ; they range in length from about 380 

 to 1970 ix and obtain a diameter of 18 /x. 



(6) The acanthostyles, when full-grown, are conically or slightly 

 basally-knobbed spicules, with recurved spines (about 3 /x highj, 

 measuring 63 to 85 /x in length, and at their base 8 /x at most in 

 diameter; the spines are scattered uniformly and pretty closely 

 over the entire surface. The slender immature spicules range in 

 length from less than 30/x to upwards of 60/x; the slenderest have 

 almost invisibly minute spines, and are provided with a well- 

 developed basal knob. 



(c)The auxiliary spicules are styli and oxea; intermediate forms 

 between these are rare or absent. The styli, which are by far the 

 more abundant, are straight or (more usually) slightly curved, and 

 taper towards the base; they vary between 280 and 410/x in length, 

 and attain to 4-5/x in diameter. The oxea are shorter and slender, 

 being very rarely more tlian 3 40/x in length, or more than 3/i in 

 diameter. Apparently the latter occur only as single and paired 

 scattered spicules in the interior; while tlie styli are found both in 

 the interior (nearly always in pairs) and in the dermal tufts. 



Loc. — Port Jackson. 



