198 PROCEEDINGS OF THE ACADEMY OF [1887. 



"3{eas. From one half inch to two inches in diameter by 

 one to one and a half lines in thickness at the centre and gradually 

 thinning off to the margin. 



"Hab. Grows upon the underside of stones below low-water 

 mark in the rivers Delaware and Schuylkill, 



"Structure. Composed of an intertexture of spiculai about one 

 four hundredth of an inch long, having a minutely tuberculatcd 

 surface, over which is reflected a granulo-cellular membrane. 



"Remarks. After the death of the sponge, the areolated tissue 

 macerates off, leaving the reproductive bodies in a close layer at- 

 tached to the rock. The living sponge is never green(?), nor does 

 it ever grow exposed to the light."(?) Leidy. 



I have thought best to preface my own description of this species 

 as seen and collected in multitudes of localities, by the above origi- 

 nal description by its discoverer Dr. Leidy. I append the follow- 

 ing from my note book: "At the Acad. Nat. Sci. January 31st. 

 1885 re-examined type specimen on a stone, of 'S. fragilis, presented 

 by J. Leidy,' taking a few spicules and statoblasts for comparison. 

 After mounting, (PI. VIII, iig. i,) I find the skeleton spicules aver- 

 age 0.0081 inches; the dermal spicules 0.0027 inches in length. 

 One four hundredth inches as given iu his description corresponds 

 with the decimal fraction 0.0025 inches ; and my measurement 

 therefore agrees very nearly with Dr. Leidy 's, of the dermal or flesh 

 spicules. He does not describe those of the skeleton." 



See further remarks as to its identification later. 



I would describe it as follows : 



Sponge varying from a nearly white to a bright green according 

 to its exposure to the light ; encrusting, in subcircular patches, thin 

 at the edges, occasionally one or more inches thick near the middle. 

 Surface smooth or more or less tuberculated ; pores and osteoles 

 numerous ; the latter sometimes one fourth inch or more in diameter 

 at the confluence of several of the larger canals. Texture more; 

 compact than that of S. lacustris. (PI. V, fig. ii.) 



Gemnudic abundant ; primarily in one or more i)avement layers, 

 generally found at the base of the sj^onge ; their foramina prolonged 

 into tubes upon the upper or outer side ; frequently curving to one 

 side but not flaring like the funnel of a steamboat. In other posi- 

 tions the gemmules are found in compact groups of varying numbers; 

 the foraminal tubules uniformly opening oiUivard. (PI. V, fig. ii, 

 B.) In all situations they are enveloped in a parenchyma of spher- 



