446 GASTEROPODA OF THE INFERIOR OOLITE. 



but Phillips' figure is characteristic. There are two varieties in the Dogger 

 which we may refer to 2\ calix. Specimens are not uncommon, but the state of 

 preservation is indifferent. 



Description (more depressed variety) : 



Height . . . . .16 mm. 



Basal diameter . . . .24 mm. 



Spiral angle about . ■ . . . 90°. 



Shell trochiform, tabulate, and profoundly excavated. "Whorls (five) nearly 

 rectangular, with a close suture. In some specimens the whorls of the spire show 

 only one keel ; but in others, where the spire is relatively higher, a lower keel is 

 exposed. The upper keel is situate at the angle, and carries the obliterated fissure- 

 band. Spiral ornament regular and in raised lines, which are somewhat wide 

 apart (see fig. 7) and ropy, the sides of the whorls being somewhat concave. 



The body-whorl exhibits a well-defined lower keel which is thick and sub- 

 angular at the periphery ; hence the bod^'-whorl is strongly bicarinate and 

 subconcave. The base is widely excavated. The aperture is depressed and 

 oblique, but the available specimens from the Dogger do not admit of any close 

 description. The loop is long and narrow, and its presence is often indicated on 

 the upper keel by a raised border. In other specimens the loop, having been a 

 source of weakness, causes a deflection in the continuity of the keel. 



The variety from the Cotteswolds (figs. 1 a, 1 h), which presents features inter- 

 mediate between T. calix. and T. affinis, has a narrower spiral angle and a larger 

 habit of growth. In some of these specimens it is possible to note the sinuous 

 character of the columellar lip. 



Relations and Distribution. — The features on which it is relied to separate 

 T. calix from its undoubtedly close relatives, T. gradus and T. affinis, are possibly 

 of little biological value. There really is very little difference except as to size, 

 and, to some slight extent, in ornamentation. The truth is that all these tabulate 

 Trochotomas are very much alike. Yet in the Dogger and partially also in the 

 Cotteswolds certain small forms or races prevail which we know as T. calix; 

 whilst in the Anglo-Norman area larger and more markedly tabulate forms, such 

 as T. gradus and T. affinis, occupy the ground. 



T. calix is fairly abundant in the ajmlinus-zone (Dogger) of Yorkshire, and 

 a very similar form, with a very thick basal rim, occurs in the opalinus-zone of 

 Frocester Hill. In the Oolite-Marl horizon (Murcliisonse-zoue) we also get these 

 small forms with the thick basal rim, as well as others of a larger size (figs. 1 a,lb) 

 where this feature is not so conspicuous. In the base-bed at Lincoln (MnrchisonaS' 

 zone) are forms showing the connection between T. calix and T. Lindonensis. 



