198 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 30, 



class such shells with Spondylus, I place it provisionally in Sowerby's 

 genus Bianchora, which forms a convenient receptacle for them till 

 their true characters are better known. 



Plate VI. fig. 4 a. Inside of under valve. 



Fig. 4 b. Side view of fig. 4 a. 



Fig. 4 c. Fragment of upper valve. 



Fig. 4 d. Fragment of upper valve of a variety with finer granula- 

 tions. 



Lima Farringdonensis, Sharpe. Pl. VI. fig. 2. 



L. testa ovata, compressa, undique radiatim costata; costis insequalibus, 

 angulatis, longitudinaliter striatis ; anterioribus subobsoletis. 



Shell transversely ovate, ornamented throughout with unequal ribs 

 radiating from the beak, which are sharply angular or slightly 

 rounded at top, and covered at their sides with fine radiating lines, 

 becoming gradually stronger towards the posterior side of the shell ; 

 anterior ribs faint, middle ribs sharp and large, with a small sharp 

 rib between each ; posterior ribs less elevated ; ears unequal. 



Length \, breadth | of an inch. 



Found in the Sponge-gravel of Little Coxwell near Farringdon, and 

 in the ferruginous sandstone of Seende near Devizes. 



This shell is very closely related to L. Cottaldina rnxd L. parallela, 

 d'Orb., and combines the small intermediate rib of tlie former with 

 the longitudinal radiation of the latter ; it differs from both in having 

 the anterior side ribbed. 



Plate VI. fig. 2 a & 2b. Natural size. 



Fig. 2 c. The same, magnified. 



Nautilus Farringdonensis, Sharpe. Pl. VI. fig. 1. 



N. testa inflata, lateraliter compressa, late umbilicata ; juniore Isevi, adulta 

 undato-subcostata ; apertura truncato-ovata, profunde sinuata; septorum 

 marginibus paululum sinuatis ; siphunculo ? 



Shell gibbous, with flattened sides, at first smooth, then crossed 

 by broad shallow undulations, which advance in a bold curve at each 

 side of the whorl and recede at the back, marking the deep sinus of 

 the mouth ; edges of the septa nearly straight ; umbilicus large, with 

 a rounded edge. Mouth broadly ovate. 



Diameter 44- inches ; width of mouth 2^ inches ; height of mouth 

 2 inches. 



From Boutcher's pit, Farringdon, where it is rare. 



This Nautilus has a flatter and more regular form and fainter un- 

 dulations than A^. undulatus, from which it is distinguished by its 

 large umbilicus ; the undulations are very faint, and in the largest 

 part of the specimen are half an inch wide each. There is no other 

 species for which it can be mistaken. The position of the siphuhcle 

 has not yet been seen. 



Plate VI. fig. 1 a & I b, reduced to frds of the natural size. 



