HELICOCRYPTUS ORSUS. 87 



are not the same as the type of that species, which, like most, if not all, Purpurinas, 

 has the direction of its body whorl at a less angle with the axis, making it appear 

 longer. Our specimens, on the contrary, are even shorter than the type of P. 

 condensate/,. 



Genus HELICOCRYPTUS, D'Orbigny. 



D'Orbigny in his ' Terrains Jurassiques,' vol. ii, thus describes a remarkable 

 small shell : " Shell depressed, orbicular, nearly coiled in the same plane. Spire 

 formed of whorls which embrace on both sides, leaving an umbilicus below and 

 another above. In the latter is a spire almost entirely hidden by the later ' whorls. 

 Mouth vertical, oval, transverse, provided inside, both above and below, with a 

 strong callosity which fills the spaces where the whorl embraces the spire, and 

 leaves the rest of the border thin." 



Helicocryptus orsus, sp. nov. Plate VIII, fig. 14. 



Type. — A specimen from Scarborough in the Sedgwick Museum, recorded by 

 Bean as Botella expansa, is not easy to locate. The following interpretation is 

 suggested : The diameter is 3'5 mm., the upper surface is smooth and shining, and 

 shows as a whole very slight convexity, so as to have the aspect of a Botella. It is 

 composed of about three whorls, each of which has a considerable depth in pro- 

 portion. They turn the angle into the under side rather abruptly. On the base 

 they all reach close to the centre and leave only a small umbilicus. Part of the 

 shell being broken through, it is seen to be very thick near the centre, but thin 

 towards the circumference. 



"Relations. — The specimen thus described does not show some of the most 

 remarkable features of the genus to which it is here referred — for the spire is 

 not sunken, and the spaces between the spire and the embracing whorls are not 

 filled up with callus. Both these, however, are abnormal features, and assuming 

 that they arose gradually from a normal shell, such, perhaps, as a Skenea, the 

 first stage of a sunk spire would be a low one, and the first stage of an infilling 

 would be a thickening of one of the walls such as are the stages represented by our 

 shell. The characters of this genus are taken from the phylogenetic adult, and 

 our shell, it is suggested, may be the phylogenetic infant. At all events, it precedes 

 the others in time. 



1 He says " precedent," but lie must mean this. 



