284 Transdctlons. — Zoology. 



As the figure shows, I give No. 1 to the columellar 

 plait, 2 and 3 to the plaits on the penultimate whorl, 4 to the 

 plait on the right lip above the keel, and 5, 6, 7 to the teeth 

 on the basal lip. The lamellae 1-4 are large, acute plaits, 

 going some distance into the interior of the shell, whilst the 



three teeth on the basal lip are only- 

 blunt elevations from a white cal- 

 losity extending from the keel to the 

 columella. Now, the type of L. 

 marina shows the lamellse 1, 3, 4 

 only, and L. nerissa 1 to 7. Amongst 

 the specimens examined, eight were 

 L. nerissa, eleven L. marina, and ten, 

 belonged to intermediate forms. The columellar plait, 1, and 

 the plaits 3 and 4 were found to be constant, never missing. 

 Plait 2 was absent in twelve adult specimens, and rudimentary 

 in seven shells, situated far back, and difficult to be seen. The 

 callosity on the basal lip was never wanting ; it could be ob- 

 served even in typical specimens of L. marina. In fifteen 

 shells there was only this callosity to be seen, without any 

 denticulation. Of the teeth 5, 6, 7, the last one is the smallest, 

 and therefore easiest reabsorbed. The teeth 5 and 6 were 

 missing in twelve specimens, but tooth 7 in nineteen. The 

 most frequently absent plait of all is 7 ; of the others, 2, 5, 

 and 6 are equally often wanting. 



The type of L. marina is only found in adult shells, 

 L. nerissa. in younger ones, which agrees well with the dimen- 

 sions of the shells as given by Professor F. W. Hutton (Trans. 

 N.Z. Inst., vol. xvi., p. 176) — 0-13in. diam. for L. marina, and 

 0-llin. for L. nerissa. 



All my observations lead me to the conclusion that in the 

 young shells all the seven plaits are developed, but are re- 

 absorbed later on in such a way that 7 first disappears, 

 followed by 2, 5, 6, thus leaving for the adult shell the plaits 

 1, 3, 4 only. 



I am of opinion that all these facts taken together show 

 clearly that L. marina and L. nerissa are but one species; and 

 this has been confirmed by examining their dentition. I pre- 

 pared the radulas of L. marina, L. nerissa, and an intermediate 

 form, but all showed the very same dentition, and there is no 

 doubt possible but that the two species must be united in 

 one. 



The name which has to be retained is Laonia marina, Hutt., 

 being that of the adult shell. The diagnosis of the shell has 

 to be slightly altered with regard to the plaits, as all the other 

 parts of the shells are very much the same in both of the descrip- 

 tions given by Professor F. W. Hutton. I propose the follow- 

 ing diagnosis : — 



