140 THE NAUTILUS. 



NOTE ON Polygyra albolabris AND P. zaleta. 

 In some regions where P. albolabris and zaleta are found to- 

 gether occasional elevated specimens of the former or depressed 

 ones of the latter occur and it is very difficult, at first glance, 

 to say to which species they belong. If, however, the shells 

 are examined under the microscope with a magnification of 

 about 25 diameters they can be readily separated, as zaleta looks 

 polished in the high light while albolabris is dull. This is due 

 to the fact that between and on the ribs of albolabris are fine, 

 vertical wrinkles in the epidermis which are absent in zaleta. 

 As a rule zaleta is also much lighter in color than albolabris, or 

 if dark specimens are found they are generally much lighter on 

 the base, and just behind the aperture there is invariably a patch 

 of much lighter color than the body of the shell. 



SOME STRTJCTUEAL VARIATIONS IN CHROMOBORIS ZEBRA. 



W. J. CROZIER. 



Contributions from the Bermuda Biological Station for Kesearch, No. 64. 



Abnormalities of a minor character are by no means uncom- 

 mon in nudibranchs, and, while these features are usually not 

 of any great morphological significance, some of them seem 

 sufficiently curious to warrant description. I have noted sev- 

 eral such deviations from the typical structure while examining 

 a large number of specimens of Chromodoris zebra Heilprin. 



Smallwood (1910) has described some of the variations in 

 the coloration of this animal, and has also referred to the vari- 

 ability shown by the branchiae, particularly in the manner in 

 which one or several of these organs terminate by division of 

 their free ends into several parts. I have elsewhere (Crozier, 

 1917) made note of the variation in the number of the glandu- 

 lar papillae which occur upon the ventral surface of the poster- 

 ior border of the mantle. 



Variation in the branchiae is, in fact, somewhat more frequent 

 and more extensive than Smallwood observed. Not unusually, 

 branchia? are to be seen which not only divide to a greater or 

 less extent at their tips, but also show a branching at some 



