290 PROCEEDINGS OF THE ACADEMY OF [1888. 



directed outward ; the lateral teeth are f^imilar, ])ut lack inner cusps ; 

 they are about eight in number, and are followed by about four 

 transition teeth ; the marginals number about fifty on either side, and 

 their cusps become more slender toward the outer edge, and the basal 

 plates shorter. A central Avith five adjacent lateral teeth, and a 

 group of transition teeth witli a true marginal tooth are shown in the 

 figure. 



Helix albella of Chemnitz, (not of Linna:;us), and H. ochroleuca of 

 Pfeifier, (not Ferussac) are, I believe, synonymous with this species. 

 The former is placed in Eurycratera in Pfeiffer's Nomenelator, and 

 the latter has been compared to Pachystyhi rufozonata, a form some- 

 what similar in characters of the shell, but belonging, of course, to a 

 distinct group. 



Poecilozonites nelsoni Bland, (jil. xvii, figs, j, k, l). 



A fossil form, differing from bermudensis in the much greater size, 

 greater number of whorls, more convex base, coarser striation, im- 

 j)ressed sutures, and especially in the peculiarly prominent dome- 

 shaped upper whorls. These are, indeed, so closely coiled as to 

 resemble a specimen of P. cirewnjirmata. The coloration,. imperfect- 

 ly shown in several specimens before me, is that of bermudensis; 

 and whilst its affinities are with the latter species, I regard it as a 

 divergent branch, rather than as an ancestor of that form. 



As has been observed in other cases of species approaching extinc- 

 tion, and probably subject to some decided and unfavorable change 

 in environment, (in this case, perhaps, due to the comparatively 

 recent subsidence and partial submergence of the island') the shell 

 exhibits great mutations and distortions of form ; sometimes the spire 

 is elevated conical, sometimes much depressed ; frequently the planes 

 of the upper and lower volutions are not parallel, and the spire con- 

 sequently is canted to one side. The species is remarkably large, 

 solid and roughly sculptured for a Zonitoid. 



Poecilozonites reinianus I'tV. (]il. xvii, figs. i). 



This heretofore unfigured species is discoidal in form, widely 

 umbilicate, the umbilicus about one-third the diameter of the base, 

 exhibiting all the whorls ; the apical whorl is smooth and whitish ; 

 the following whorls are quite convex, with deep sutures, l)rownish, 

 very prettily zigzagly flammulate with chestnut color, like many of 

 ihe species of Pahila. The body-whorl in adult examples is round- 



1 See Challenger Report, Narrative, vol. i, p. 138. 



