1898.] NATURAL SCIENCES OF PHILADELPHIA. 433 



in others they are much more evident, or may be entirely wanting. 

 Some of this type are straight, but most are more or less curved, 

 those surrounding the oscula being often semicircular. The ends 

 may be simply pointed, or variously enlarged, and either smooth or 

 roughened with minute spines as shown by a few examples in 

 Plate XX, figs. 2, 3, 4 and 5. The dermalia consist of sword shaped 

 hexacts, which are so numerous as to suggest the specific name of the 

 species. Like the diacts, these differ much in the relative develop- 

 ment of the several limbs, any of which may be straight or more or 

 less curved or even sharply bent. Fig. 9 shows the most typical 

 proportions, but the handle may be scarcely longer than the blade 

 or not more than | as long. The cross pieces may be straight or 

 curved, or sharply bent upward (Plate XX, fig. 12). The handle 

 differs most, being slender and pointed, club-shaped or knobbed, and 

 usually sculptured throughout or at the tip only. The points of 

 the other rays are also usually spinose. The sword handles support 

 the skin, and are not furnished with floricomes at their distal ends ; 

 instead they are surrounded by bundles of minute acicular diacts, 

 Plate XX, fig. 7. 



The hypodermalia are regular hexasts, oxy-hexasters, which have 

 the principal rays prolonged (Plate XX, fig. 8), rosettes wdiich vary 

 in the length of the principal rays, as shown by two examples in 

 Plate XX, figs. 14 and 15, and discohexasters of great beauty and 

 symmetry of form. One of the simplest of the latter is shown in 

 Plate XX, fig. 16. This has the principal rays well developed, while 

 each group of terminal rays has sixteen members, the pin-head 

 shaped disks having again 16 marginal teeth. Other discohexasters 

 have the number of terminal rays much greater, or the principal 

 rays shortened, so that all appear to arise from a central sphere. 



The gastralia are also sword-shaped hexacts without bundles of 

 accessory acicular spicules. This sponge would appear to be the 

 type of a new subfamily of Euplectellida?. 



Description of Plates. 



Plate XIX. Hyalodendron navalium n. s. The type specimen as 

 it appeared when first taken, from a drawing by a 

 Japanese artist, x f%. 



Plate XX. Illustrating some of the forms of the spicules of 



Hyalodendron navalium. 

 Fig. 1. One of the smaller simple diacts of the kind which make 

 up the interior skeleton of the spines and processes, and 



