392 W. H. Sudleston — Gasterojjoda of the Portland Rocks. 



6. Chemnitzia teres, sp.n. Plate XL Figs. 3a, 35. 



Description. — Specimen from the Cyrena-heds of Chilmark Quarry. 



Length 35 millimetres. 



Width 16 



Length of body-whorl to entire shell 46 : 100. 



Spiral angle 35". 



Shell moderately elongate, conical, subturrited, not umbilicated. 

 The spire increases under a regular angle of 35°, and consists of 

 about nine whorls (seven preserved), which are well separated by 

 the suture. The posterior portion of each whorl is distinguished by 

 a rounded projection or belt, which serves to conceal the suture, and 

 gives a somewhat turrited aspect to the spire ; the whorls have a 

 shallow submedian excavation. Body-whorl smooth and regular, 

 with a slight excavation in the posterior third. The entire shell is 

 devoid of ornament (in its present condition) other than faint lines 

 of growth on the body-whorl. Aperture ovate ; columella but little 

 excavated, and not much covered by callus ; no trace of an umbilicus. 



Belations and Distribution. — This very pretty and regular species 

 is most nearly related to Melania ahhreviata, Eoem. (Ool. Geb. p. 159, 

 pi. X. fig. 4), subsequently recognized and described by De Loriol 

 (Jurass. Sup. de Boulogne, vol. i. p. 80, pi. viii. figs. 2 and 3) from the 

 Sequanien of Bellebrune, and noticed by me as occurring in the Lower 

 Calcareous Grit of Cumnor, near Oxford. It especially resembles 

 that species in the prominent belt at the posterior margin of each 

 whorl, which almost conceals the suture. It differs from that species 

 in its rounder and softer outlines, in the inferior value of the spiral 

 angle, and in the regularly conical form of the spire. The belt at 

 the posterior border, which characterizes all the whorls up to the 

 very apex, may serve to distinguish it from other species of the so- 

 called Cbemnitzias. 



This form is tolerably abundant in the Ci/rewa-beds of some parts 

 of the Vale of Wardour, but the state of conservation is usually 

 indifferent. It has not been found elsewhere, as far as I know. 



7. Chemnitzia naticoides, sp.n. Plate XL Figs. 10a, 106. 



Description. — Specimen from the Oj/rena-beds of Chilmark Quarry. 



Length 20 millimetres. 



Width 12 „ 



Length of body-whorl to rest of shell 57 : 100. 



Spiral angle 50°. 



Shell sub-conical, moderately elongate, not umbilicated. Spire 

 composed of about five whorls, smooth, well-defined by suture, and 

 increasing regularly ; no belt distinguishes these whorls, which are 

 slightly excavated. The body-whorl is scarcely tumid, and has a 

 shallow depression in the upper third, which gives emphasis to a slight 

 and well-rounded median keel. Aperture ovate to semilunar : not 

 the least trace of an umbilicus. 



Belations and Distribution. — There is really so little to lay hold 

 of in a shell of this sort that its affinities can only be guessed at. It 

 may indeed be a dwarf of some form already known in other 

 countries. Both it and the next described form are found sparingly 

 in the Cyrewa- beds of the Vale of Wardour. 



