210 PROCEEDINGS OF THE ACADEMY OF [1887. 



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

 _|. 9e 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 

 oi- rounded, smootli 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 

 ;^haft erect and the other rotule forming, or projecting beyond the 

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



The existence of birotulate spicula (then called amphidisks) in 

 t he crust surrounding the gemmulse of some sponges was first pointed 

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

 cluiracteristics of SpongUla fluviat'dk; thus distinguishing that species 

 from ;S'. lacustris, witli which until that time it liad been constantly 

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

 species possessed the same peculiarity, Mr. 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 diffused throughout 

 tlie world ; and its leading species, M. Jiuviatilis, 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 approximate determination of the several 

 species. 



KKY TO THE SPFXIKS OK THE GENUS MEYENIA. 



(a) Margins of birotulate spicules entire. 



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

 birotulates upon the surface of the gemmulte covered with a 

 deej) parenchyma of lai-ge cells. 



Meyenia, ( Trochospongilla) erenaeeus. 



2. Skeleton spicules smooth, short, robust; margins of short birotu- 

 lates exjiected; each gemmule enclosed in a capsule of skeleton 

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



'^. Rotulie large, fiat; gemmules furnished with an envelope charged 

 with spined spicules. M. gregaria. 



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



M. minuta. 



