336 MISS MCDONALD AND DR. TRUEMAIS' OX [vol. IxxVli, 



spirals which are somewhat more pronounced in the wide sutural 

 region. There is a tendency also in these later whorls for the 

 posterior portion to be moulded on the preceding whorl with the 

 formation of a concave sutural area. (Compare fig. 18 b. p. 330.) 



This species may be regarded to some extent as constituting 

 a morphic equivalent of Z. subrugosa ; doubtless a similar ten- 

 denc}^ towards the shallowing of the sutural region and the 

 embracing of the whorls is to be found in both divisions of the 

 Loxonematidse. 



Locality and horizon.- — Our specimen was found in the 

 Lower Lias (^annatus zone) of Binces' Lodge, Wilton (Somerset), 

 and is in Mr. J. W. Tutcher's collection, No. 1038. A somewhat 

 similar specimen (PI. XXII, fig. 7). in which the ribs of the later 

 Avhorls are more curved, was found by Mr. Tutcher at the same 

 horizon at Clandown Quarry, Kadstock (J. W. Tutcher coll., 

 No. 1008). 



YI. Othee Liassic Tueeiculate GtASTEOPODS. 



Family MATHILDIID.E Cossmann. 

 Peomathildia Andrese. 



This genus includes a number of species showing considerable 

 differences in ornamentation and shape, which resemble one an- 

 other in having an elongated shell, a holostome aperture, fre- 

 quently^ angular, and heterostrophic embryonic whorls. 



In most of the species spirals appear before axials, and are more 

 important than the axials in the ornamentation of adult whorls ; 

 several species tend to be strongly carinate. Examples of the 

 genus are not common in the Liassic rocks of this countrj^ for which 

 reason it is not proposed in this paper to suggest any grouping 

 of the species. 



Peomathildia texuicostata (Portlock). (PL XXII, fig. 6.) 



CeritJiium tenuicostatum Portlock (14, p. 124). 



C. tenuicostafum Tate (21, p. 15). 



Dimensions of a tyjjical specimen. 



Length. Sreadth. Length of spire. 



5 mm. 30 per cent. 60 pei" cent. 



Small slender forms, with holostomatous aperture and hetero- 

 strophic embrj^onic whorls ; spiral and axial ornamentation fine, 

 with the exception of three anterior spirals which are much 

 stronger. 



Development. — After the smooth heterostrophic embryonic 

 whorls, the first ornamentation to appear is a single spiral occupy- 

 ing an antero-raedian position ; verj' fine curved axials soon make 



Spiral 



Sutural 



angle. 



angle. 



20° 



115° 



