210 PROCEEDINGS OF THE ACADEMY OF [1887. 



though that is so much further south, the range is far greater, from 

 -f 96° to — 20° or— 24° Fahr.; with an annual average of 44°." 



(II) Gen. MEYENIA, Carter, Ann. and Mag. etc. 1881, p. 90. 



Gen. Char. Skeleton spicules acerate, curved, fusiform, pointed 

 or rounded, smooth or variably spined. Gemmules globular or oval, 

 enveloped in a granular crust, charged with birotulate spicules (PI. 

 IX, b. b. etc.) of a single class or type, radially arranged; i. e. with 

 one rotule resting upon or approximating to the chitinous coat, the 

 shaft erect and the other rotule forming, or projecting beyond the 

 surface of the gemmules. (PI. V fig. v and vi.) 



The existence of birotulate spicula (then called amphidisks) in 

 the crust surrounding the gemmulae of some sponges was first pointed 

 out by F. J. F. Meyen, (1839) who made them the distinctive 

 characteristics of Spongilla fluviatlUs; thus distinguishing that species 

 from S. lacustris, with which until that time it had been constantly 

 confused. In his generic revision of the group, finding that several 

 species possessed the same peculiarity, JNIr. Carter, with excellent 

 taste, grouped under the name of Meyen those that exhibited this 

 feature in its simplest conditions. 



Next to Spongilla in importance, as it follows it in our classification, 

 the genus Meyenia appears to be the most widely diflflised throughout 

 the world; and its leading species, 31. fiuviatilis, like S. lacustris is 

 found exhibiting many variations, to perplex the student and tempt 

 him to the creation of unnecessary names. The following is pre- 

 sented as a guide to the a2:)proximate determination of the several 

 species. 



KKY TO THli SPKCIES OF THE GENUS MEYENIA. 



(a) Margins of birotulate spicules entire. 



1. Skeleton spicules covered with powerful spines. Spool-like 

 birotulates upon the surface of the gemmultje covered with a 

 deep parenchyma of large cells. 



Meyenia, ( Trochospongilla) erenaceus. 



2. Skeleton s{)icules smooth, short, robust ; margins of short birotu- 

 lates exflected; each gemmule enclosed in a capsule of skeleton 

 spicules. (PI. V fig. iv, PI. X, fig. i.) M. leidyi. 



H. Rotulse large, flat; gemnmles furnished with an envelope charged 

 with spined spicules. M. gregaria. 



4. Gemnuiles about one fourth the size of those of other species. 



3L minuta. 



