122 



"TERRA NOVA" EXPEDITION. 



and Ostraconotus * — may fairly be said to have become carcinized. It would be natural 

 to expect that these three genera would be closely related, but, in fact, that is not the 



case. As res^ards the mode of reduction of the 

 abdomen, Tylasins and Ostraconotus do show 

 some resemblance, though the process has been 

 carried much further in the latter genus than in 

 the former. In both of them the abdomen is 

 straight and slender, and carries its unpaired limbs 

 in the usual position on the ventral side. But 

 when the appendages of the male are regarded it 

 becomes evident that Tylaspis belongs to the 

 group of genera which have paired limbs on the 

 forepart of the abdomen (in point of fact it has 

 two pairs), whereas Ostraconotus resembles Eupa- 

 gurus in having no paired pleopods at all. The 

 condition of Porcellanopagurus in this respect is, 

 as we have seen, at present still a little doubtful, 

 but in any case, with its unique arrangement in 

 the female of three limbs dorsally placed in a 

 slanting row, it is obviously the result of an 

 entirely different process from that which produced 

 either of the others, so that, even if there were 

 any grounds on which it could be supposed to be 

 related to one of them, its carcinization must have 

 occurred independently. The cephalothorax tells the same tale. In Tylasjns the soft 

 hinder region found in an ordinary hermit-crab has become inflated and then 

 hardened.! In Ostraconotus the whole cephalothorax has taken something of the 

 shape of that of a Galatheid, the hinder region being hardened as in Tylasp)is. In 

 Porcellanopagurus, while the hinder region remains soft, the 

 forepart is quite unlike that of either of the others, as will be 

 gathered from the description I have given of it. In the shape 

 of the legs there is again the widest difference between the 

 three. The sole point of resemblance between them lies in the 

 fact that the last leg of each has the same minute, clumsy, 

 spoon-fingered chela, and this they share with other Eupagurinae. The fourth leg is 

 subchelate in Porcellanopagurus \ simple, with a wide propodite for the protection of 



ElG. 11. — Eupagurus splendescens : 

 outline dorsal view, X 2J-. 



Fig. 12.— End of fourth 

 leg of Tylaspis, X 7|. 



* For descriptions and figures of these crustaceans, see Henderson, "Challenger" Anomura, p. 81, 

 pi. VIII, fig. 5, 1888 {Tylaspis), and Milne-Edwards and Bouvier, Mem. Mus. Harvard, XIV, iii, p. 167, 



pi. XII, 1893 {Ostraconotus). 



f This is also the case in Eupagurus splendescens. 



