92 



BIOLOGICAL SURVEY OF 



spicular fibers running longitudinally are found. Spicula are 

 slightly curved, rather gradually tapering oxea, 0.19 to 0.21 

 mm." (Lundbeck.) This species is erected on six 'more or 

 less damaged' fragments of a couple of specimens. 



R. hyalina. ''Erect, leaf-shaped. The dermal membrane 

 without spicules; the ends of the fibers projecting, and the 

 surface consequently finely shaggy. Oscula? The skeleton 

 a regular network of primary and secondary fibers, the fibers 

 unispicular. Particular polyspicular longitudinal fibers are 

 found. Spicula are slightly curved, evenly tapering oxea, .261 

 to .31 mm." (Lundbeck.) This species rests on 'only one 

 specimen,' which is, moreover, a 'fragment.' 



The length of the spicules in these species is here presented 

 for comparison in the following table : 



Less than 



These differences in the lengths of the spicules are very 

 small and form a finely graded series. This fact along with 

 the few specimens which have been studied, the similarity of 

 regions, and continuity of their distribution make it seem 

 probable that these four species may only be varieties or geo- 

 graphical races of a single species. 



Topsent gives .245 to .265 mm. as the length of the spicules 

 in a specimen of Reniera ventilabrum, and this measurement 

 renders less significant the differences in spicule length which 

 alone seems to be the criterion for their separation. In organ- 

 isms so responsive to their environment such small variations 

 as the descriptions indicate, as well as the minute differences 

 in spicule length, will undoubtedly be shown upon further 

 study to fall within the limits of normal variation for a single 

 species. 



