December, 19 12. The h'ish Naturalist, 225 



NOTES ON THE DEVELOPMENT OF ACTAEONIA, 



SHEWING THAT A. CORRUGATA OF AldER AND HaNCOCK 



is but an immature stage of their 

 Cenia (Actaeonia) Cocksii. 



by nathaniel colgan, m.r.i. a. 



Examination of a large series of Actaeonias taken in 

 tidal pools at Bullock on the shores of Dubhn Bay, between 

 the months of January and March, 1909, first led me to 

 doubt the existence in this genus of the two species usually 

 referred to it in works on the Britannic marine fauna. 

 A further study of the development of Actaeonia from 

 the ^g'g up almost to full maturity raised these doubts to 

 a conviction that the two species were in fact nothing 

 more than different stages in the growth of one and the 

 same organism. It would be presumption to set aside, 

 save for the weightiest reasons, a dehberately expressed 

 opinion of authorities so eminent in all that relates to the 

 British Nudibranchiate Mollusca as are Alder and Han- 

 cock, the authors of these two species ; so it will be necessary 

 to give here at some length the evidence which seems to 

 me to justify the fusion of Actaeonia corrugata with A. 

 Cocksii. 



Both of these species were, for the first time, described 

 and figured in the Annals and Magazine of Natural History 

 for June, 1848, in a paper by Alder and Hancock, entitled 

 " On a proposed new Order of Gasteropodous Mollusca." 

 Here one of the species was assigned to the genus Actaeonia 

 under the name Actaeonia corrugata, while the other, 

 dedicated to its discoverer, Mr. Cocks of Falmouth, became 

 the type of a new genus, Cenia, under the name Cenia 

 Cocksii, Cenia being suggested to the founders of the genus 

 by the ancient name of Falmouth, where the animal was 

 first discovered. Subsequently, in Vol. V. of Jeffreys' 

 British Conchology, pubhshed in 1869, Alder, the surviving 

 author of the genus Cenia, fused it with Actaeonia, Ceitia 

 Cocksii thus becoming Actaeonia Cocksii. 



Comparison of the descriptions and figures of the two 

 species of Actaeonia shows that the distinctive specific 



A 



