56 THE VOYAGE OF H.M.S. CHALLENGER. 



my opinion the smaUness of i be form, the totally different shape of the eapitulum, and its 

 living exclusively on the carapace of turtles are sufficient characters for regarding it 

 as a true species. I give a figure of this form on PI. II. fig. 13. It is represented by a 

 considerable number of specimens, which are all very small, none having a eapitulum of 

 the size of half an inch, the greatest length observed by Darwin. The parts of the mouth 

 air exactly as in Conchoderma virgatum. In one of the specimens I investigated, 

 however, the left hand mandible is malformed in a curious way (having seven teeth 

 without the inferior angle), whereas the right hand mandible looks exactly normal. I have 

 figured both mandibles on PI. II. figs. 14 and 15. These parts, as is well known, often 

 show anomalies of more or less importance. 



These specimens were taken from the carapace of a CJielone, between Gibraltar and 

 Madeira, January 31, 1873. Darwin says that it is only found on the Testudo caretta; 

 whether this is the only turtle on which it lives I cannot say. With regard to the 

 smaUness of this variety, I must add that I got specimens from the Eoyal Museum of the 

 Netherlands (labelled "on Chelone, lat. 35° N., long. 14° W. "), wdiich w T ere much 

 larger, and even larger than the size given by Darwin (13 mm.), the length of the 

 eapitulum being almost 18 mm. 1 



Fresh evidence of the great variability of this species is furnished by the study of 

 specimens of this species from the Gulf of Naples. It is the form of the valves, and 

 especially of the scutum, which in these specimens shows a very interesting deviation from 

 the typical form, the three lobes of the scutum not being broad but narrow, as in the 

 Conchoderma hunteri, Owen, sp., and the carina which is also much more slender. As this 

 very narrowness of the valves is t ,the most distinctive character by which the latter species 

 can be distinguished from Conchoderma virgatum, the study of the Mediterranean form 

 has confirmed my opinion that it is by far the safest way at present to accept only two 

 species, and to consider all the other forms as varieties. 



Alepas, Sander Rang, 1829. 



With the exception of one species, Alepas parasita, Sander Rang, which measures 

 two inches, all the species of this genus are rather small. They are found attached to 

 various living objects, fixed or floating. Alepas parasita has been always taken on 

 Medusas, Alepas minuta, Philippi, lives attached to a Cidaris, Alepas cornuta to an 

 Autipathes, Alepas tabulosa, Quoy et Gaimard, to a living Palinurus. 



Off New South Wales, the Challenger collected some specimens of a species of this 

 genus, which were attached to the spines of an Echinid {Phormosoma). 



The little group of Lepadids which constitute this genus is sharply defined by the 

 following characteristics : — The eapitulum is either without valves, or with horny almost 



1 The size is no doubt a very bad characteristic. I received specimens from the Gulf of Naples of Conclmlerma 

 virgatum as well as of Conchoderma auritum, both remarkable for their smaUness. 



