22 Mr. J. Lycett on the Fossil Conchology of the 



Commencing with the upper portion of the Great Oolite in our vicinity, 

 we find several beds of hard limestone and bands of marly clay, containing 

 a series of shells representing in diminished numbers the inhabitants of the 

 lower and richer fossiliferoua beds of the formation. Several which 

 do not occur in the lower group I will notice ; these are the little 

 Cardium Beaumont i (Archiac), very abundant, Pholadomya nana (Phillips), 

 Chemnitzia, new species, Bulla Hildesiensis (Rcemer), Bulla suprajurensis 

 (Reamer), Cardium pes-bovis (Archiac), Cardilla grandis, new species. The 

 other forms which commonly occur are Lucina lyrata (Phillips), Lucina 

 rotundata (Rcemer), Ceromya semi-striata, new species, Ceromya excentrica 

 (Isocardia, Rcemer). We have been fortunate enough to succeed in clearing 

 the hinges of the two latter species, and have thus ascertained that they 

 have nothing in common with Isocardia, but belong to the new genus 

 Ceromya of Agassiz. Isocardia conccntrica must likewise be placed in the 

 same genus. 



Quitting these beds and descending through sandstones nearly destitute 

 of organic remains, we arrive at the shelly Oolite locally termed planking, 

 or upper beds of the Great Oolite building stone, a marine deposit distin- 

 guished by the great profusion of its fossil conchology and their good slate 

 of preservation. Here at one locality we find a large assemblage of a genus 

 which seems to be characteristic of this formation and especially of this 

 vicinity; I allude to the new genus Purpuroidea, of which the generic 

 characters are as follows : — 



Shell turreted, ventricose, apeture large, apex of the spire pointed. 

 Spire consisting of several whorls usually convex, and having about their 

 middle part a circle of tubercles or blunt spines. Columella smooth, 

 rounded, and curved inwards at its base. Notch wide, but not deep nor 

 recurved. Outer lip thin, slightly sinuated, and forming an acute angle 

 posteriorly at its junction with the body whorl. The casts of the interior 

 are smooth, or exhibit but faint indications of the tubercles, and none of 

 the ribs or striae which distinguish the perfect shells. The axial umbilicus 

 is usually very conspicuous and the basal notch not distinguishable. They 

 would certainly be taken for Natica 1 by persons not conversant with the 

 outer form, and even appear to have been figured as such by Rcemer under 

 the title of Natica subnodosa from the Oolite of Hanover. One of the 

 species has twice been imperfectly figured in English works ; first in Young 

 and Bird's "Geology of the Yorkshire Coast," as Merux nodulatus; the 

 figure is merely a rude sketch of a bad specimen, but characteristic ; sub- 

 sequently a figure representing little more than a cast was given in the 

 u Mineral Conchology," as Merux tuberosus. The varieties of form and 

 markings which two of the species exhibit are worthy of notice; the most 

 abundant shell, P. rugosa, when young and the size of a nut, has tubercles 

 in lieu of spines ; the transverse ribs are well-dt fined ; but the longitudinal 

 elevations which give the species a rugose aspect are absent, the basal notch 

 is nearly obsolete, and the columella is nearly straight. The P. nodulata has 

 still greater varieties ; when full-grown it has two encircling rows of 

 tubercles on the body whorl, from the lower and smaller of which proceed 

 oblique longitudinal ribs which terminate in a transverse elevated basal 

 belt. The young shell is nearly 6mooth ; the smaller circle of tubercles 

 is scarcely distinguishable ; the ribs are absent, as is likewise the basal belt. 

 Occasionally in full-grown specimens the smaller circle of tubercles 

 degenerates into an encircling rib. The spire is of various degrees of 

 elevation, in fact scarcely any two specimens are exactly alike ; a considerable 

 number are therefore desirable for its full elucidation. The third species, 

 P. glabrata, is rare; it equals the others in magnitude. It is seldom that 

 we can trace the limits of a species over any particular area; here however 

 we are enabled to do so with tolerable accuracy. These shells are grouped 

 together in the blocks of stone by hundreds, occupying a vertical thickness 

 of 6 or 6 feet, and spread over an area 50 yards wide and 100 long. It is to 

 he regretted that this prolific space will ere long be entirely removed, and 



