162 



ON THE KADULA AND MAXILLA OF OXYSTYLA UNDATA 



(BRUG.). 

 By Hev. E. W. Bowell, M.A. 

 Bead 12th June, 1914. 

 In a specimen of this species' placed at my disposal by Mr. B. B. 

 Woodward the extended radula is 10"2mm. long and 8'5mm. wide. 

 It has 162 transverse rows of unci, and tlie middle row has 120 on 

 each side of the central. The posterior margin is convex, the sides 

 parallel, and the anteiior margin semicircular. In consequence of 

 the convexity the rows begin early to take an oblique direction, and 

 a line of arrested growth in the anterior third of the specimen shows 

 that all unci in each row become operative at the same time, so that 

 the part pi'esenting in the oral cavity has the appearance of an 

 inverted V. The maxilla is sharply arched below in correspondence 

 with this form ; it is composed of imbricated plates in two series, 

 a fundamental row with vertical direction as in normal Helicids, and 

 a superimposed oblique row ; the central or sub-central lamella of 

 this row forms the triangular piece described by Binney as 

 characteristic of Orthalicinae. 



»r*/* 



The fusion in my specimen was very thorough, none of the plates 

 being separable after maceration in hypochlorite solution. This form 

 of maxilla is probably secondary to the wide oblique-rowed radula, 

 and I suggest that this is the essential Orthalicine character. The 

 radula precedes the maxilla in developmental history. 



The appended sketch shows the curious unci of Orthaliciis. The 

 enlargement of the apices seems to have brought about tlie obliquity 

 of the rows ; enlargement of the alse is found in cases where the 

 opposite kind of obliquity occurs (e.g. in Succinea, Punctum). And 

 this enlargement of apices may be directly occasioned by the breadth 

 and bluntness of the cones ; no apex, but extended ala, is found in the 

 numerous multicuspid unci of Pectinibi'anchs and small Pulmonates. 



' Often referred to as Orthalicus zebra (Miiller). 



