CCELOCION. 191 



parietal wall, and a palatal fold within the penult, whorl. 

 Dextral. 



Perrieria from western New Guinea would seem from the 

 inadequate descriptions and figures to be imperforate, though 

 the axis may be tubular within. The two species now known 

 are sinistral, and neither has a parietal lamella. The internal 

 structure is unknown. It seems necessary to signalize by 

 name the diverse structures of the umbilicate, internally 

 lamellate Australian type, at least subgenerically. The un- 

 coiling of the latter part of the last whorl is a feature of 

 senile degeneration in the Queensland Ccelocion, not shared 

 by the New Guinea Perrieria. 



The radula of P. australis from Warroo, Port Curtis (pi. 

 31, figs. 4, 5), has 20.1.20 teeth. The central teeth are as 

 wide as the laterals, and have a single wide cusp, shorter 

 than the basal-plate. The laterals have a wide mesocone and 

 a small ectocone. The 8th to 10th teeth are transitional to 

 the marginals, which are wide, with the basal-plates short as 

 usual, and the ectocone is conspicuously bifid. The jaw (pi. 

 31, fig. 6) is arcuate and nearly smooth, showing some ex- 

 tremely weak vertical striae. 



The internal closing apparatus of Ccelocion is inexactly 

 paralleled by that of Holospira and Sectilumen in the Uro- 

 coptidae, and by Distoechia, Thomea, Cceliaxis, etc., in the 

 Stenogyroid Achatinidae ; but none of these genera has two 

 axial lamellae. 



In Ccelocion the axial lamellas are apparently the columel- 

 lar and subcolumellar (pi. 30, fig. 28, front, and f. 29, back 

 view of the same shell) . The supracolumellar lamella, pres- 

 ent in Megaspira and Eomegaspira, is absent. The subcolu- 

 mellar lamella penetrates higher up than the columellar. The 

 young shell has a basal plica, absorbed with further growth ; 

 but a series of shells from young to adult may possibly show 

 that the palatal plica of the full-grown shell is a continuation 

 of the basal plica of the young. The palatal plica is a struc- 

 ture Ccelocion has in common with Eomegaspira. 



The precocious development of the lamellae and plicae in 

 the young stages, by acceleration, gives evidence of the long 



