236 PROCEEDINGS OF THE ACADEMY OF [1887. 



with the present variety as, according to the reports of the collector, 

 the masses could not have been submerged for a greater period than 

 six weeks in any one year. "Whether the whole bulk as now seen 

 was attained during a single season, or is the cumulative result of 

 several annual growths of the persistent masses, cannot now be de- 

 termined. (See description of Parmida brownii.) 



It is worthy of notice that 31. plumosa and this variety, Y.palmeri ; 

 differ from all other known fresh-water sponges by the presence in 

 them of a compound or substellate dermal spicule. The spicule of 

 the dermis throughout the group are generally minute, spined acer- 

 ates ; in M. everetti, Mills, we find them as minute birotulates. 

 In this species the two forms seem to be combined ; the spines have 

 become central and prolonged, while their capitate extremities 

 suggest the rotules of the last-named species. 



Of the six sponge masses from the above locality, sent by the 

 Smithsonian Institution for examination, the smallest was some- 

 what fusiform in shape and proved to belong to a different si^ecies, 

 Meyenia crater iformis, Potts, heretofore found along the eastern 

 border of the United States. In it alone, the mass was not dark_ 

 ned by the presence of some pervading vegetable parasite. 



(Ill) Gen. HETEROMEYENIA, Potts. 

 Proc. Acad. Nat. Sci. Phil., 1881, p. 160. (PI. VI, fig. i.) 



Gen. char. Skeleton spicules and gemmulse as in Meijenia ; the 

 latter surrounded by intermingled birotulates of two classes, gen- 

 erally differing in form, and whose shafts are of unequal lengths. The 

 proximal disks of all rest upon the chitinous coat ; the outer ex- 

 tremities of the less numerous class projecting beyond the others. 



This genus now covers at least three well defined species, "svith 

 several marked varieties, and represents a type or modification of 

 Mexjenia unknown to Mr. Carter at the time of the preparation of 

 his system. It was founded in 1881 upon the discovery of H. repens 

 and H. argyrosperma at Lehigh Gap, Pennsylvania ; and its neces- 

 sity was confirmed shortly after by the addition of JET. ryderi, and 

 its several varieties. It will be seen by the genus definition that it 

 is not intended to embrace mere irregularities in the positions or in 

 the length of gemmule-birotulates, such as may sometimes be found 

 in M. everetti or 3f. subdivlsa ; nor yet to include biserial or tri- 

 serial arrangements of them. In each of the three principal species 

 described there are essential differences, not merely in the length 

 but in the forms of these birotulates; those of the longer class in 



