1887.] NATURAL SCIENCES OF PHILADELPHIA. 243 



of rotules nearly as great as the length of the shaft ; margins lacin- 

 ulate or crenulate, outer surfaces flat, symmetrical, often micro- 

 spined ; terminations rounded. (PL XI, fig. v, c,d, etc.) 



3{eas. Skeleton spicules 0"0127 by O'OOOG inches. Long birot- 

 ulates 0-0023 by 0-00025 inches. Diameter of disk 0-0006 inches. 

 Length of short birotulates 0-0012 inches ; diameter of its disk 

 0-0009 inches. 



IIo,b. Timbers, stones, etc., in shallow flowing water. 



Log. Found from Florida to Nova Scotia, and from the Atlan- 

 tic coast to Iowa, United States. 



H. ryderl alone, of this genus, has been found large enough to at- 

 tract the attention of a casual observer ; inclining to form upon 

 plane surfaces, hemispherical or dome-shaped masses several inches 

 in diameter. In these and other cases they are made up of a con- 

 geries of lobes or rounded prominences. It was first found in the 

 year 1881, rather plentifully, within a limited space upon the rocky 

 bottom of Indian Run, a very" small stream in the neighborhood of 

 PhiLadelphia, Pennsylvania. The following year it was missing, 

 and I have never since found it in that stream. It has been gath- 

 ered or received from at least nine American States mostly along 

 the Atlantic coast from Nova Scotia to Floiida, but including one 

 remittance from the western state of Iowa. The finest specimen 

 collected was from the timber side of the fore-bay of E. Doughty's 

 mill, Absecum, New Jerse}^ This was about three inches in diam- 

 eter and more than two inches in thickness.^ 



H. ryderi has furnished me with my latest and most valuable les- 

 son in group classification. Until quite recently the species stood 

 compact, or with only the single suggested variety, S. baleni, where 

 the spicular features were similar, though more slender, and the 

 general form of the sponge had not been particularly observed. 



^ The circumstance above mentioned as tg the failure to find this species at 

 the same place during successive seasons, is a peculiarity of habit only too famil- 

 iar to sponge collectoi"s. However reliable their recurrence may be in /a^es or 

 ponds, in our smaller streams the fact that a species was found at a given locality 

 during one season, furnishes no guarantee for its reappearance there during the 

 next. When any sponge is found, the probabilities are rather in favor of its belong- 

 ing to a different species. In the present case, a year or two later, I found, a few 

 yards further down the stream, not H. ryderi hut Tubella pennsylvanica. From 

 my favorite locality for Carterius latitenta, a friend, who undertook to bring me a 

 fresh specimen, two or three years after its first discovery, sent me a fine form of 

 S. lacustris ; and so they go, constantly moving down stream; one species suc- 

 ceeding another as they travel on to the great sea and there — 



