500 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



TOL. 39. 



greatly in length, indeed a considerable variation exists in individual 

 zooecia of the same zoarium. For convenience this portion is called 

 the stolon. The true zocecial, and therefore specific characters can 

 be expressed only in those portions of the zoarium lodging mature 

 animals. Obviously the slender stolons of the typical species of 

 Corynotrypa could not lodge normal polypides, and this portion is 

 consequently deemed of subordinate specific value. The stolon may 

 be said to correspond to the immature zone of a zooecium in a tre- 

 postomatous bryozoan. The normal polypide undoubtedly was lim- 

 ited to the expanded portion of the zooecium (2) which is here desig- 

 nated as the zooecium proper or simply the zooecium. This portion 

 has several characteristics which are very constant within specific 

 limits. First, and taxonomically most useful of such characters, is 

 the size of the zooecia, which, when the variable stolons are eliminated, 

 is remarkably constant. The angle of divergence of a zooecium (g), 

 obtained by measuring the rate of expansion of its sides from the 



s <. 



Fig. 2.— Characteristic species of Corynotrypa, X20, illustrating variation in stolon (s) 



ZOOECIUM PROPER (z), AND ANGLE OF DIVERGENCE (g). a, CORYNOTRYPA DELICATULA; 6, C. ABRUPTA; 



c, C. curta; d, C. inflata; e, C. turgida. 



distal end of the stolon, has likewise proved of much value in identi- 

 fying the different types. Less useful criteria, and generic rather 

 than specific in significance, are the position and relative size of the 

 zooecial aperture and its encircling peristome. As a rule the aperture 

 is subterminal and has a diameter about one-third that of the zooecium 

 at its greatest width. The walls are similarly porous in this as well 

 as in many other cyclostomatous genera, so that the minute structure 

 of the walls offers little help in distinguishing either species or genera. 

 However, one section of Corynotrypa contains species in which the 

 walls are transversely wrinkled so that the character of the zooecial 

 surface is, therefore, not to be entirely ignored. 



In brief, then, after determining from its uniserial growth and 

 clavate zooecia that a form belongs to this new genus, the species may 

 be determined almost wholly by the size and general outline of the 

 zooecium proper, and, under the latter, especially by its angle of 



