390 7F. II. Iludleston — Gasteropoda of the Portland Boclcs. 



proportional measurements in so rugged a shell. The height of the 

 bodj'-whoi'l is evidently considerable in proportion to the rest of the 

 spire, and the sides preserve the same slope. A very strong keel 

 is developed a little above the middle of the whorl, to which it thus 

 imparts an angular character. The upper part of the whorl is exca- 

 vated, whilst the anterior portion tapers rapidly to the base. The 

 entire shell is ornamented with broad transverse ribbing, probably 

 decussated by fine longitudinal (i.e. transverse to the axis) lines : in 

 the body-whorl this transverse ribbing is subdivided by what looks 

 like exaggerated lines of growth. Shell substance very thick : 

 aperture oval to semilunar. Scarcely a trace of iimbilicus. 



Relations and Distribution. — This very curious shell might almost 

 be taken as the type of these Natico-Chemnitzoid forms, having 

 affinities with Pseudomelania percincta, on the one hand, and with 

 Natica incisa, next to be described, on the other. The general con- 

 tour of the shell, and especially the strong median keel, connects it 

 with the first named, and the almost total absence of an umbilical 

 groove is a further bond of union. On the other hand the aperture is 

 more naticoid, and the rugose habit of the shell rather serves to connect 

 it with Natica incisa. If we are to I'egard it as a Natica, it may be 

 looked upon as exhibiting an extreme phase of the angular varieties 

 of that genus, and in the great development of the median keel it 

 affords an instance of the tendencies of the period, felt in more than 

 one group of shells, and which received its supreme expression in 

 Neritoma sinuosa. 



No other specimen has yet been found. 



4. Natica incisa, Blake, 1880. Plate XI. Figs. 4a, 4&. 



Natica incisa, Blake, 1880, Q.J.G.S. vol. xxxvi. p. 229, pi. ix. figs. 1, la. 



Bibliography, etc. — This species was first noted by Mr. Blake in 

 the " creamy limestones " of Coney Hill and Quainton in Bucks, 

 associated with Natica ceres, Lor., to which he considered it to be 

 somewhat nearly related. 



Description. — Specimen from the 0?/rema-beds of Alford Quarry, 

 near Tisbury. 



Length 26'5 millimetres. 



Width 22 „ 



Length of body-whorl to entire shell 70 : 100. 



Spiral angle 88°. 



Shell ovate, subangular, moderately umbilicated. Spire rather 

 short, with sharp apex : it consists of about five whorls, separated 

 by a well-marked suture ; posterior margin of each whorl flat and 

 indented. Body-whorl large, subangular, and characterized by a 

 broad depression running longitudinally {i.e. transverse to the axis 

 of the shell) along the upper part, so as to produce a slightly 

 bicarinated appearance. The deep sulci on the tabulate posterior 

 margin of the whorls may be traced across the flanks of the shell ; 

 between these are finer lines of growth : general aspect of the 

 ornamentation slightly rugose (often softened down by action of 

 solvents), with traces of fine longitudinal lines. Aperture wide 



