388 



MISS MCKOXALD AM) DE. TRTJEMAX OX [vol. Ixxvii, 



Fig. 23. — Promathildia liga- 

 turalis. Holotype x 4. 



Holotype : A specimen in the Museum of Practical Geology, Jermyn Street, 

 London, No. 7961. 



A slender form, with angular 

 whorls ornamented bv spirals and 

 wideh^-spaced axial folds. 



The development cannot be made 

 out ; the ornamentation charac- 

 teristic of the shell consists of two 

 spirals, the highest of which forms 

 a carina on the anterior third of 

 each whorl, and a double sub-sutural 

 band near the jDosterior suture. 

 The space between the spirals is 

 smooth, except for a slight wrinkl- 

 ino; caused by distant axial folds. 



This species, from its resemblance 

 in form and ornamentation to 

 P. ihex, is referred to Proma- 

 thildia^ although the embryonic 

 whorls have not been seen. 



Locality and horizon. — The 

 holotype is a specimen from the 

 Lower Lias of Redmile (Lincoln- 

 shire). 



Peomathildia teigemmata (Wilson). 



Cerithium trigemmatum Wilson (27, pi. v, figs. 10 & 10a). 



Dimensions of our specimen. 



Length. Sreadth. Length of spire. 



4 mm. 37 per cent. 75 per cent. 



Small slender shells, with more or less angular whorls, ornamented 

 by three rows of tubercles, the lowest set forming a well-marked 

 anterior carina. The outline of the oral region in our specimen 

 shows no indication of the presence of a canal, and we infer that 

 the mouth is holostome. 



Development. — The embryonic whorls are smooth and 

 heterostrophic. The first ornament to appear, so far as can be 

 made out, consists of two spiral bands, the stronger of the two 

 occupying an anterior position ; almost immediately axial ornament 

 appears, and tubercles are produced at the points of intersection. 

 By the fifth whorl a faint third spiral is intercalated, and the 

 remainder of the shell is ornamented by three rows of equally- 

 spaced rounded tubercles of unequal size, the anterior set of which 

 forms a well-marked carina. An extra spiral is added on the last 

 whorl beneath the carina. 



As has been ah*eady noted, our specimen is holostomatous, but 

 Wilson described the aperture of his specimen as having a faint 



Spiral 



Sutuval 



angle. 



angle. 



24° 



99° 



