CER1THIUM. 149 



Goldfuss, and Gerithium (Cryptaulax) tortile, Heb. and Desl., which was clearly a 

 mistake, as these two are totally different species. He was not so far wrong in 

 including Melania undulata, Deslong., as this is certainly in part a representative 

 species. The same author also regarded Chemnitzia ? vetusta, Morris and Lycett, 

 as a species distinct from that of Phillips, and already included under C.flexuosum, 

 Minister. 



Description. — Size variable; 15 mm. is the length of a fair-sized specimen. 

 The spiral angle is about 18°. Shell elongate to elongate-ovate. Spiral angle 

 regular; whorls ten to twelve, flat to subconvex, anterior whorls turrited, suture 

 close. The posterior whorls are very flat, with longitudinal costae, which are 

 straight and extend from suture to suture, almost without spiral decussation. 

 By degrees the whorls become more convex, the costae becoming arcuate, and in 

 very well-preserved specimens decussated by fine spiral lines, which cause the 

 costae to be granular. 



In full-sized specimens the body-whorl is slightly ventricose, and, if well pre- 

 served, the spiral decussations are shown; in this case the uppermost row of 

 spirals assumes a slightly muricated character. Base full and spirally striated, 

 with sometimes a slight prolongation of the axial costae. Aperture broadly ovate, 

 with a sharp angle at the posterior extremity ; inner lip somewhat expanded on 

 the columella ; anterior canal fairly developed (in all available specimens the end 

 of the canal has been broken off). 



Varieties. — The original figure of Terebra vetusta, Phil., represents a specimen, 

 either from the Millepore or Grey Limestone, which is in that condition where all 

 the fine spiral lines are obliterated. This is perhaps the most usual condition for 

 specimens. It is partly on account of this appearance that Terebra vetusta has 

 "been so often referred to " Chemnitzia." 



Chemnitzia ? vetusta, Phil., of Morris and Lycett, represents a more perfect 

 specimen from one or other of the same beds. The spiral ornaments are faintly 

 distinguishable, more especially in the anterior whorls, and the longitudinals are 

 somewhat more arcuate. Hence Braun's reference to Cerith. flexuosum. In the 

 Dogger this stage of C. vetustum is not uncommon. 



So much as regards Yorkshire varieties. Elsewhere in the Inferior Oolite of 

 England there are specimens, some with granular, some with continuous costae, 

 straight or flexed, which may be referred to C. vetustum. I have several such 

 from the Parlcinsoni-zone of the Cotteswolds. When in bad condition C. vetustum 

 is the most suitable name. 



Relations and Distribution. — Under the head of relations little more need be 

 said. As regards distribution, C. vetustum occurs in the Dogger, where it probably 

 represents an incomplete stage of the next species. The best specimens, as 

 regards condition, are obtained from the Lower Division of the Scarborough 



