506 



PROCEEDINGS OF TEE NATIONAL MUSEUM. 



VOL. 39. 



four are in the collections of the U. S. National Museum, and their 

 study, in connection with numerous other examples, soon revealed 

 the fact that this extreme variation is due, not to the zooecium 

 proper, but to the stolon. Single zoaria were found exhibiting, 

 in individual zooecia, all the differences attributed to the supposed 

 four distinct species. Such a zoarium is shown in figure 4, in which 

 the usual relation between the length of the stolon and the zooecium 



proper is shown at a. At h the 

 stolon is almost entirely absent, 

 but the zooecium has the normal 

 shape, size, and angle of diver- 

 gence. However, zooecia in the 

 same linear series, as at c, may 

 develop stolons of considerable 

 length. It will be observed in 

 each of these cases that the size 

 and shape of the zooecium prop- 

 er, and its angle of divergence, 

 in addition to such characters as 

 the position and size of the ap- 

 erture, has remained constant. 

 The stolon is obviously the va- 

 riable character, and, elimina- 

 ting it, one can not attribute 

 such unusual variability to these 

 simple types as has been done. 

 The cause of this variable de- 

 velopment of the stolon seems 

 to be a purely physical one, due 

 almost entirely to the habitat 

 of the species. For instance, 

 again using the example figured 

 above, the zooecia at a are in- 

 crusting a smooth plane sur- 

 face; at h there is a depression just wide enough to accommodate a 

 short zooecium, while at c the surface is sfightly roughened, and the 

 zooecium, to avoid this unfavorable spot, develops a stolon of greater 

 length. 



CORYNOTRYPA DELICATULA (James). 



Hippothoa delicatula James, Paleontologist, no. 1, 1878, p. 6. 



Stomatopora delicatula Nickles and Bassler, Bull. U. S. Geol. Surv., no. 173, 



1900, p. 419.— Bassler, Proc. U. S. Nat. Mue., vol. 30, 1906, p. 55, pi. 3, 



figs. 4-7. 

 Stomatopora proutana Miller, Journ. Cincinnati Soc. Nat. Hist., vol. 5, 1882, 



p. 39, pi. 1, figs. 4-46.— Ulrich, Geol. and Nat. Hist. Surv. Minnesota, 



Final Rep., vol. 3, pt. 1, 1893, p. 117, pi. 1, figs. 8-12. 

 Rhopalonaria pertenuis Ulrich, Fourteenth Ann. Rep. Geol. and Nat. Hist 



Surv. Minnesota, 1886, p. 59. 



Fig. 4.— COEYNOTRYPA DELICATULA. ZOARIUM, X12 

 ILLUSTRATING VARIABLE LENGTH OF STOLON. Or- 

 DOVICIAN, CORRYVILLE BEDS OF McMlLLAN FORMA- 

 TION, Cincinnati, Ohio. For lettering see 



TEXT. 



