TROCHUS. 377 



body- whorl into one thick nodular belt. In this form, also, the umbilicus is, for the 

 most part, more completely closed, whilst the ornaments are softer in outline and 

 less disposed to be spinous. Specimens are obtained from the lower part of the 

 Yeovil Sands at Bridport Harbour in the Dumortieria-beds, and more rarely in the 

 Opalinus-zone of Burton Cliff. 



This tendency to fusion of the duplex carina is also noticeable in certain fine 

 specimens of T. duplicatus from the Parkinsoni-zone of Powerstock, Broad- 

 windsor, &c. 



314. Trochus subduplicatus, var. Abbas. Plate XXXII, fig. 1. 



Description : 



Height . . . . .24 mm. 



Width . . . . .21 mm. 



Spiral angle ..... 55°— 60°. 



Shell regularly conical, scarcely umbilicate ; spire elevated, in most cases 

 considerably exceeding half of the total height ; apex sharp. Whorls seven to 

 eight, very concave, and distinctly separated by a considerable suture. There is 

 a nodular carina at the posterior and anterior margin of each whorl, the anterior 

 one being usually compound ; fine and regular spiral lines ornament the hollow 

 portion of the whorls. 



The body-whorl is much excavated and similarly ornamented, the nodular 

 anterior carina being excessively thick and complex. The base is rather inclined 

 to be flat, and is decorated with fine spiral lines throughout, which are more or 

 less puckered by coarse radial lines converging towards the very slight umbilical 

 fissure. Aperture subrhomboidal and slightly depressed, with a considerable callus 

 on the inner lip. 



Relations and Distribution. — In this very beautiful and highly ornamented shell 

 we scarcely recognise our old acquaintance of the Dumortieria-beds. The inter- 

 carpal spaces, instead of being smooth, are full of spiral lines, which are also 

 conspicuous in the base ; the base likewise is flatter and the aperture more 

 depressed. In the general figure there is some approach to T. duplicatus, but in 

 no other respect. 



Trochus Abbas is characteristic of the Concavus-hed at Bradford Abbas. I have 

 one specimen from Burton Bradstock, horizon unknown. It may at once be 

 distinguished from the Dumortieria-hed fossils by the fine spiral ornamentation in 

 all stages, by its flatter base and larger habit of growth. 





