66 THE NAUTILUS. 



T. marmorea was rather uncommon as indeed I found it through- 

 out. On this spot 1 dredged the form described below one adult 

 and one half grown in 1899, and a young specimen in 1901. 



Tonicella ruler (Lowe) var. index, nov. 



In every respect typical except in color, 1 which is in life an ivory- 

 white slightly tinged with green (taking on in alcohol or formol the 

 exact appearance of old ivory tinged faintly with yellow,) highly 

 polished and absolutely unmarked except for a few extremely faint 

 and minute light pink dots on the posterior edges of the mid-valves 

 and a very conspicuous dark purple elongated triangle pointing 

 posteriorly on the keel of the fifth valve. Girdle very pale, other- 

 wise typical. 



A color variety connected with the typical form by intermediate 

 stages is perhaps not worth describing, but this form, while clearly 

 close to typical ruber, appears to be quite discontinuous. Dr. Dall 

 pronounces it new to him, which is practically to say new to science. 2 

 In spite of the fact that the mark on the fifth valve is often recog- 

 nizable in typical specimens (and is probably present in all, though 

 disguised by the strong color-patterns) and in spite of the fact that 

 very pale, almost white, valves frequently occur and sometimes (as 

 Dall has noted) to the number of four or five in a single specimen, 

 yet the present variety can be distinguished from any other specimen 

 of ruber I have ever seen, across an ordinary room. It is not a mere 

 case of faintness of the rosy marking!?. The markings are wiped 

 out and a totally new color scheme (viz. green) introduced. My 

 three specimens, dredged two years apart, are absolutely indis- 

 tinguishable except for size. The first specimen dredged was adult 

 (probably hatched the year previous) the last very young (probably 

 breeding the next year.) It is, therefore, not connected with age 

 and has persisted on the same spot probably for at least four years; 

 but is not a true geographical race (in the sense, for instance in 

 which ornithologists use the term) since it is a cohabitant with the 

 typical form. 



What, then, is T. ruber var. index? It may be pathological, or a 

 " physiological variety " an albino in short but it's local persist- 



1 Radula not examined. 



2 In this connection Chiton marmoreus var. cceruleus Winkley should be con- 

 sidered. See NAUTILUS VIII, p. 78, 1894. ED. 



