- NORTH AMERICAN PORIFER^. PART II. 523 



broad. Both this species and sub-species gossypina have a tendency to grow up into rotund 

 forms, which are, however, smallest at the base, and sometimes quite contracted at this 

 point, especially if the object or area to which they are attached is small enough to limit 

 the growth of the diameter of the base. The varieties are many, though not of a mark- 

 etable character, and therefore not so well known to spongers as those of gossyp'ma. 



Loc, Biscay ue Bay, Nassau, in Soc. Coll. 



One very remarkable specimen exists in the Collection of the Academy of Natural Sci- 

 ences of Philadelphia, about a foot high and a foot broad at the base. It is a huge pile, so 

 to sjjeak, of the single fistular forms, like a bee hive. The depressions between the cone- 

 like orifices are very deep and irregularly arranged in lines from the base to the summit. 

 The surface is, however, the most interesting part. The primary fibres project in bundles 

 of small size, very evenly distributed over the entire surface. They are both larger and 

 longer than the similar bundles in the adult forms, and resemble closely those of sub- 

 species cerehriformis. It required a close examination of many specimens in order to 

 show any essential differences of surface, though the adults of these two forms are very 

 distinct in this respect. 



Loc, Bahama Islands. 



It is not 23ossible to distinguish some of the varieties of the Hard Head from those of 

 the Yellow sponge. The irregular forms and looser textured varieties approximate to 

 those of the sub-species eorlosia, both in structure and aspect, and this is the case also with 

 the young of many varieties in both series. 



Sub-species punctata. 



In this sub-species (PI. xvi, fig. 23), the typical specimens have often a close resemblance 

 to sub-species fubuUfera in form ; and the almost total absence of the larger primary bun- 

 dles with their interstitial channels, increases this resemblance ; the apertures are also fre- 

 quently deeply indented on the outer side, as in that species. This form, however, is 

 denser than any other, and the bristly minor bundles are in greater profusion and of 

 greater length than in other varieties. The apertures also are more numerous than in 

 the preceding variety, and about three-eighths of an inch in diameter. They open also 

 superficially, instead of being buried in the channels between the large projecting cushions 

 of the skeleton. 



Loc, Nassau, in Soc Coll. 



Variety densa. In this variety (PI. xvi, fig. 27) all shades of difference and transition 

 are represented, until we come upon a form which is identical with sub-species eorlosia. 

 This can, however, like other varieties, be distinguished from that species by the number 

 and small size of the apertures, their scattered distribution over the whole surface, and the 

 toughness and darker color of the skeleton. The minor or superficial bundles of bristle-like 

 fibres are hardly seen at all on the upper side of some specimens, and in all they are much 

 less marked than in the preceding variety. This gives the upper surface a jiarticularly 

 smooth or even aspect, which is, however, broken up by numerous sujoerficial anastomosing 

 canals, which become more or less parallel upon the sides. 



Loc, Nassau, in Soc. Coll. 



In all of these varieties the forms may vary greatly. In the first they seem quite 

 constantly club-shaped, or at least round clumps taller than they are broad, and narrower 



