443 



NOTES ON PROSOBRANCHIATA. 



No. iii. — The Neanic Shell of Melo diadem a, Lamk., 



AND THE Definition of the Nepionic Stage in the 



Gasteropod Mollusc. 



By H. Leighton Kesteven. 



(From the Biological Laboratory, Sydney University). 



A. Neanic Shell of Melo 'diadema, Lamk. 



(1) Description of shell and mass of egg-capsules. 



(2) The succession of the columellar folds. 



B. Definition of the Nepionic Stage in the Gasteropod Mollusc. 



(1) A comparison of Molluscan stages of development with those of the 



Lepido2)tera. 



(2) Three types of transition from Embryonic to Neanic shell-structure, 



and suggestions as to their explanation and significance. 



(3) Conclusions arrived at. 



C. A SHORT LIST of WORKS IN WHICH PROTOCONCHS ARE DESCRIBED, OR IN 



WHICH THE AUXOLOGICAL TERMS ARE DISCUSSED. 



A. Neanic Shell of Melo diadema, Lamarck. 



Description of shell and mass of egg-capsules. — The following 

 remarks are to some extent inspired by a short note by Mr. B. B. 

 Woodward* on the nepionic shells of 31. i^idicus, Gmel., in a recent 

 part of the Proceedings of the Malacological Society. His note 

 led me to examine similar specimens of J/, diadema, Lamk., and 

 apices of many other Volutes; and I have arri\ed at the conclusion 

 that it is probable that the formation of adult structure within 

 the egg-capsule is common to many of the Volutidte, if not all. 



* Woodward, Proc. Malac. Soc. Lond., v., No. 4, 1803, p. 260. 



