WATSON : ANATOMY OF OCHTBEPHILA. 283 



artery, a vessel wliicli passes downwards between the sub-cerebral 

 commissure and tbe broad and sbort anterior pedal commissure. 

 To some of the arteries with wbich it is in contact tbe sub-cerebral 

 commissure seems to give off one or two pairs of very slender nerves. 



The sub-cerebral commissure is quite as well developed in these 

 three species as in any of the sigmurethrous snails in which I have 

 observed it, and it is probable that it will be found also in other 

 orthurethrous forms. Indeed, I believe that I have seen it in 

 Pleurodiscus flavidus (Rossm.) [=: Patulastra halmei (P. & M.)] 

 and in Acunthinula aculeata (Miill.), although I have not been 

 successful in following it throughout its entire length in these 

 species, and should not yet like to state definitely that it is 

 present. It is very likely, however, that this slender commissure 

 will be found to occur generally throughout the Orthurethra. 

 Thus the evidence now before us would seem to point to the 

 conclusion that in the Pulmonata there are normally five com- 

 missures passing beneath the alimentary canal, namely, the buccal 

 commissure, the sub-cerebral commissure, the two pedal com- 

 missures, and the visceral commissure ; but of these the narrow 

 sub-cerebral is, of course, the only ventral commissure that unites 

 the cerebral ganglia directly, without the intervention of any other 

 ganglia. 



Summary. 



A slender sub-cerebral commissure is now known to unite the 

 cerebral ganglia beneath the alimentary canal not only in half-a- 

 dozen families of sigmurethrous snails, but also in at least three 

 orthurethrous genera, namely, Ena, Rachis, and Chondrina. It is 

 probable that it is present also in other genera of the Orthurethra, 

 and that there may normally be five ventral commissures in the 

 Pulmonata. 



THE ANATOMY AND GENERAL AFFINITIES OF OCHTHEPHILA 

 (= GEOMITRA) TURRICULA (LOWE). 



By Hugh Watson, M.A. 



Read Sth June, 1923. 



PLATE VI. 



(1) Anatomical Description. 



The following account of the anatomy of Ochthephila (Hystricella) 

 turricula (Lowe) ^ — otherwise known as Geomitra turricula ^ — is 



1 Trans. Cambridge Philos. Soc, vol. iv, 1831, p. 58, pi. vi, fig. 21. 



- In 1895 Pilsbry discarded the name Ochthephila Beck, 1837, in favour of 

 Geomitra Swainson, 1840, because he thought that the former generic name 

 was too like Ochthiphila, a name which Fallen had given to a genus of flies 

 in 1823 (see Man. Conch., ser. ii, vol. ix, pp. 238, 239, 243). But Pilsbry wrote 

 before the establishment of the International Rules for Zoological Nomen- 

 clature ; and it is clear from the recommendations of Article 36 of this 



