106 PEOCEEDINGS OF THE NATIONAL MUSEUM vol.81 



served in specimens A-C, either at the rim of the oscular margin or 

 in the lateral wall of the entire stock. But in the remaining speci- 

 mens, long, diactinic prostalia project beyond all parts of the outer 

 surfaces. They do not occur in large numbers nor do they form a 

 definite fringe at the oscular margin (except in specimen F), though 

 they are more abundant in the upper portion of the sponge than 

 elsewhere. These marginal and pleural prostalia are smooth on the 

 surface, frequently reach a length of 20 mm and have a maximum 

 thickness of about 180/x. 



The hypodermalia are strongly developed diactins, oxypentactins 

 with paratropal paratangentials and pentactins. There are usually 

 in each grouj) one or two pentactins that have entirely smooth para- 

 tangentials, except at the ends; they may be the youngest of all in 

 the group. The older pentactins (fig. 14, a) usually are situated at 

 a higher level than the younger (this is characteristic of all Rhab- 

 docalyptus species) and have the paratangentials armed from base 

 to tip with strong, straight or slightly curved, and sharply pointed 

 prongs, arranged in two series along the lateral sides of the rays. 

 The prongs are placed at fairly regular intervals, those of the two 

 sides alternating with one another. In the basal parts of the rays, 

 the strongest prongs may be 119/^ long; there they all spring out 

 vertically, frequentlj'^ bend forward away from the dermal surface. 

 Toward the tip of the rays and along with the gradual tapering of 

 these, the prongs grow continually smaller. Apart from the above 

 prongs, the surface of the paratangentials is perfectly smooth, except 

 at the microtuberculated end. The unpaired shaft ray is occasion- 

 ally pronged, but then not so numerously as in other rays. The 

 paratangentials of the older pentactins are 20 mm to 50 mm long, and 

 the shafts 40 mm to 90 mm. The rays are not more than 85/>t thick 

 at the base. 



The dermalia are predominantly pentactins (fig. 14, c), which 

 have short, rough, microtuberculated tangential rays 90/^ to lOOju, 

 long; proximal ray T5/t to 85^ long. Less often, among the der- 

 malia, stauractins are found lying with their rays in the dermal 

 plane and still more rarely hexactins somewhat smaller than those 

 in the gastral layer. 



The gastralia are rough hexactins (fig. 14, 5) with rays exactly 

 like those of the dermalia ; length of rays, 152/^ to 190/a ; breadth at 

 base, 12ju,. Occasionally all six rays in the same spicule are subequal, 

 though in most cases the proximal ray is somewhat longer than the 

 paratangential and the distal rays. They measure 152/* to 176/a in 

 length. The microtubercles are slightly more pronounced on the 

 proximal ray than on any other. 



The oxyhexasters occur in abundance in all parts of the sponge 

 wall and are of three slightly differing forms, designated herein by 



