328 



MISS MCDONALD AoS^D DE. TRrEMAX 0]S" [vol. Ixxvii, 



Zygopleuea deleta, sp. nov. (Text-fig. 15.) 



Cf. Chemnitzia nuda Tate (24, pi. x, fig. 9). 



Dimensions of holotjpe (estimated). 



Breadth. Length of spire. ^^ j 



^ ./ -r angle. 



Length. 

 30 mm. 



25^ 



Sutural 

 angle. 



Fig. lo. — Z3'goplem'a deleta, 

 sj). nov. Holofype x 2. 



29 per cent. 80 per cent. 



Holotype : Specimen now in the Department of Geology. British Museum 

 (Natural History), G. 24869. 



A large form with feeble costse giving place to veiy faint curved 

 striae. The Avhorls are convex, with a slight angularity near the 

 posterior suture. The mouth is incomplete ; oval. The holotype 

 is slightly crushed. 



Develo lament. — The shell is incomplete, and all the apical 



whorls are missing ; but the earliest 

 whorl preserved appears to be 

 smooth, while the next is sub- 

 costate. During the succeeding 

 whorls, however, the costse become 

 fainter, and the last whorl is orna- 

 mented by faint curved growth- 

 lines only. 



This form ma}^ be regarded as a 

 eatagenetic development from some 

 form resembling Z. cf. hlainviUei. 

 Among the gastropods from the 

 tunnel-heaps at Old Dalby are 

 found several examples interme- 

 diate between Z. cf. hlainviUei and 

 Z. deleta, in which the ribs are 

 confined to the middle and upper 

 whorls, but become obsolete on 

 the last whorl; the series from Z. cf. hlainviUei to Z. deleta 

 shows progressive increase in size. 



The species just described differs from Turritella nuda Miinster, 

 chiefly in the absence of spirals, and from GJvemnitzia nuda Tate, 

 in the different curve of the striae and the slightly angular whorl. 



Locality and horizon. — The holotype is a specimen from 

 the Lower Liassic clays, from the tunnel-heaps at Old Dalby 

 ( Leicestershire ) . 



Zygopleuea >s^uda (Tate) non Miinster. (Text-fig. 16, p. 329.) 



Cf. Chemnitzia nuda Tate (24, pi. x, fig. 9). 



Dimensions of holotype (estimated). 



Length,. 



27 mm. 



JBreadth. 

 30 per cent. 



Length of spire. 

 77 per cent. 



Spiral 

 angle. 



20° 



Sutural 



angle. 



103° 



Holotype : A specimen in the Tate Collection, Museum of Practical Geology, 

 Jermyn Street, London, No. 7993. 



