100 MOLLUSCA FROM THE GREAT OOLITE. 



B. Species with the spire depressed and mammillated. 

 A. CYLINDEICI. 



CYLINDRITES GYLINDRICUS. Plate VIII, figs. 19, 19a, b, c. 



C. Testa cylindricd, elongatd, truncatd; spird depressd, vel obsoletd, vertice sulconcavo; 

 anfractibus angulaiis, anfractu ultimo margine superiore acuto. 



Shell cylindrical, lengthened, truncated; spire depressed, almost obsolete j vertex rather 

 concave ; volutions angular, the last one with the upper margin acute. 



This is the most elongated and truncated species of the group, and might easily be 

 mistaken for a specimen with an imperfect spire : in well-preserved specimens the apex may 

 be observed to consist of two volutions, which rise above the others, forming a mammillated 

 summit; the base of the shell is much contracted and lengthened. 



Locality. It is rare, and has been found only in the "planking" of Minchinhampton 

 Common. 



CYLINDRITES EXCAVATTJS. Plate VIII, figs. 17, \la, b. 



C. Testa cylindricd, truncatd; spird inversd, apice mammillato, vertice mac/no profunde 

 excavato; anfractibus numerosis, marginibus acutis notatis; anfractu ultimo subconvexo, 

 margine superiore acuto, subcontract; ceteroB nota desunt. 



Shell cylindrical, truncated; spire inverted; apex mammillated, vertex large, deeply 

 excavated ; whorls numerous, their upper margins acute ; the last whorl somewhat convex, 

 with an acute margin, and slightly curving inwards. Base not seen. 



The specimen being rather imperfect at the base prevents our ascertaining with 

 exactness the length of the species, which would appear to be intermediate to C. bullatus 

 and C. Thorcntei, but is certainly less elongated than the latter species ; the vertex is large 

 and very deeply crateriform, the apex not rising much above the centre of the deep con- 

 cavity, and not so high as the margin of the last volution, the edges of the numerous whorls 

 being visible in the concavity. 



Locality. This example and a section of another are all which have been obtained ; 

 they occurred in the upper series of the Great Oolite formation, a little higher than the 

 hard cream-coloured limestone, and in a rock of nearly equal compactness, two miles east 

 of Minchinhampton, on the road to Cirencester ; the same rock, also, contains C. acutus 

 and C. angulatus, but the intractable nature of the material renders it extremely difficult to 

 obtain good specimens. 



