31^6 MISS MCDOXALD A^D DE. TETJEMAX 0>' [vol. Ixxvii, 



Strongly costate with widely-sepai-ated ribs ; later forms in each 

 series become more finely ornamented, and the axial ribs become more 

 ciiryed with, in some cases, a return to the smooth condition ; ^vhile 

 other species, especially those in the Upper Lias, haye imbricate 

 whorls. 



ZxGOPLEUEA sp. (Text-lig. l-i a , p. 327.) 



Dimensions ■ estimated j of om' specimen. 



-r J.J -D jj,7 7- J.1 -p ■ spiral St'tural 



Lienqth. Breadth. L,enqth of spire. ^ n ^ 



^ J ./ _r angle. angle. 



10 mm. 45 per cent. 75 per ceut. 25° 105' 



Fairly slender -liell : Ayliorls flat, separated by faint sutm-es, and 

 ornamented Ayith straight, coarse, widely-separated axial ribs. 



Deyelopment. — Little can be said concerning the deyelop- 

 ment of this indiyidaal, for the earliest whorls are not present, and 

 all those preseryed are similarly ornamented with simple ribs, as 

 above described. 



This species, if we jndge from its simple ornamentation and 

 low horizon, most probably represents the primitiye stock that 

 ultimately gaye rise to the series of simply-ribbed Zygopleura. 



Locality and horizon. — The specimen described is from the 

 Rhsetic at Bine Anchor, and is in the collection of Mr. J. W, 

 Tiitcher, Xo. 1009. 



Ztgopleuea cf. TEAXsyEESA (Blake). 



Cf. Chemnitzia transversa Blake (1 ; also 24, pi. x, fig. 21). 



Dimensions of our specimen. 



Length, Breadth. Length of S])ire. 



o'o mm. 36 per cent. 72 per cent. 



Small slender form, with flat whorls separated by rather feeble 

 sntures ; the ornamentation consists of widely-separated, slightly- 

 curyed, axial ribs. 



Deyelopment. — Three ap)ical whorls cjuite smooth, fourth 

 whorl ornamented by about seven thick straight ribs ; in the later 

 Avhorls the axial ornament becomes yery slightly curved. 



The only point of difl:erence between this form and the form 

 preyiously described is the curyature of the axial ribs. 



Locality and horizon. — The specimens were collected from 

 the Lower Liassic clays on the tmmel-heaps of Old Dalby 

 (Leicestershire), and are now in the collection of the Geological 

 Department, ITniyersity College, Xottingham. 



Ztgopleeea cf. BLAixyiLLEi (Mllnster). (PL XXII, fig. 1 & 

 text-fig. 1-Ic, p. 327.) 



Cf. JtTelania blai/ivillei Miinster (7, pi. cxcviii. fig. 9). 



Cf. Cerithiuni henrici ^Martin (10, pi. ii, figs. L7-18). 



Cf. Chemnitzia henrici Moore (11, pi. xvi, tig. 12). 



Cf. Chemnitzia jpoUymiaca Dumortier (5, pt. 1, 1864, pi. xviii, fig. 9). 



Sjpiral 



Svtural 



angle. 



angle. 



23= 



110- 



