A. 0. DiMON 33 



and apical anglo vary inverseli/ as t.hc lerigth. Hence " spxirious coi-relation " 

 occurs, and \ve should (/ priori, cxpect index and angic to be ncgatively corrclatcd 

 with length and posiüvcly corrclatcd with cach other. The corrclatioii of dianictcr 

 and length would havo to bc dctermined in Order to nieasure the ainouiit of 

 " sjuiridus ciiri'i'latioii " lictwecn index and length. 



(10) Descriptioii of Ahnoriiutl Siiail. About one hundicd shells froMi caoh 

 localitv wcrc incasured wliile the aninials inhabiting thetn wcrc still alivc, and 

 of this luuaber one aninial was seen with the left tentacle double and boaring two 

 eyes, as rcpre.sented in Figiire 4. All the rest of tht^ s])ecinicus wcrc killed before 



Fig. 4. Freehand outline sUetcli uf snail froni locality 2. 



measuring, and as the foot was retracted, the tentacles could not be seen. No 

 other sport of any kind was observed. Bate.son ('S)4) has reported cases of doubling 

 of tentacles and eyes as follows : Patella vidgata, tentacle and eye repeated on 

 the left side ; Flij/sa acuta, riglit tentacle bitid ; three cases of a snpernumerary 

 eye without donbling of the tentacle; and one case {subemarginula) where both 

 eye-stalks were double, and eaeh bore a supernumerary eye. This condition, then, 

 would secm to be not uiicomnion, and is mentioned and figured merely as adding 

 one more to the cases of siniilar abnormality alreail}- known. 



Suminarij. 



I. Therc are in Cold Spring Hai'bor and vicinity two species of Nassa, with 

 no forins intermediate in all characters, though tlieir habitats ovei'lap. 



II. When eompared with the normal types for the species, both thcse species 

 are depauperatc, bcing smaller, more globose, with a larger aperture in proportion 

 to their length, more obtuse apical angle; and in the case of N. obsületa, fewer 

 whorls. This dcpauperization is connected with the .slight density of the water in 

 Cold Spring Harbor, as eompared with the open oceau. 



III. If the three lots of N. obsoleta be eompared with one another, those 

 from within the harbor are seen to be more depaupei'ate than those nearer its 

 mouth. This depauperization is also connected with the density of the water in 

 the three localities from which the specimens were cullected. 



Biometrika n 5 



