274 PROCEEDINGS OF THE ACADEMY OF [1887. 



Fig. V. Meyenia fluviatilis. Surface of gemmule. "Crust" charged 

 with "birotulate" spicules (amphidisks) ; one star-shaped 

 "rotule" resting upon the chitinous coat, the other pre- 

 sented to the observer, or more or less foreshortened. (See 

 PI. IX, fig. iii, etc.) 



Fig. VI. Meyenia craterijormis. Section of chitinous coat of gem- 

 mule, supporting-6, hooked "birotulates" with very long 

 shafts ; whose positions, normally radial, are, in this spe- 

 cies, frequently twisted or confused. (PI. X, fig. v.) 



Plate VI. 



Fig. I. Heteromeyenia argyrosperma. Partial section of "chitin- 

 ous coat" and "crust" of gemmule, showing : — a, the 

 somewhat narrowing "foraminal aperture ;" thick "gran- 

 ular crust" charged with-6, "long" and-6\ "short" birot- 

 ulate spicules. (PI. XI, fig.'i and ii.) The outer rotules 

 of the longer birotulates, when covered by the crust, form 

 conical protuberances as figured. They are, perhaps, more 

 frequently seen naked. 



Fig. II. Ttihella pennsyhanica. Partial section of chitinous coat 

 of gemmule, surrounded with granular crust ; in which 

 are embedded,-^, minute, incequibirotulate spicules, (PL 

 XII, fig. i, ii, iii.) the larger rotule always resting upon 

 the chitinous coat. The thickness of the "crust," in this 

 species, varies in different localities, from barely equalling 

 the height of the spicules, to the extreme of covering them 

 two or more times that depth. 



Fig. III. Carterius tubisperma. Partial section of chitinous coat 

 and crust of gemmule; the latter embedding-6, birotulate- 

 spicules. Foraminal aperture prolonged into a long tu- 

 bule-a, flaring and funnel-shaped at its extremity and 

 divided into several short tendrils or cirrous appendages,- 

 d. 



Fig. IV. Cai'terius stepanowii. Partial section of gemmule showing 

 protoplasmic contents, crust, birotulate spicules-6, foram- 

 inal tubule-a, penetrating the subquadrangular, flange- 

 like extension-c?, divided at the angles into numerous very 

 short cirrous appendages, (after Dybowski.) 



Fig. V. Carterius latitenta. Partial section of chitinous coat, bear- 

 ing crust, and birotulate spicules-6 ; and extended into a 



