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



description of the species, that the posterior pedicels in several forms of the family 

 Elpidiidje as, for instance, in Scotoanassa diaphana, Scotoplanes insignis, Elpidia 

 willemoesi, &c, are webbed together by a thin skin, which gives to these forms a most 

 peculiar appearance. Besides, it must not be forgotten that the posterior pedicels in 

 Parelpidia elongata differ from the anterior, elongate, cylindrical ones, and present a 

 form peculiar to themselves ; these posterior pairs of pedicels (PL I. figs. 3 and 4), are 

 large, flattened, oar-shaped, taper towards their tops into an acute point, while the odd, 

 hindmost, and very flattened pedicel attains a considerably greater breadth and has its 

 obtuse end incised. The lateral pedicels in the family Elpidiidse vary considerably as 

 to their position and deserve special attention. They are, for instance, more thinly 

 scattered anteriorly than posteriorly, where they are commonly crowded close together, 

 side by side. The genera Parelpidia and Peniagone, excepting Peniagone affinis, 

 Elpidia purpurea, Elpidia verrucosa, Scotoplanes robusta, Scotoplanes insignis, and 

 Scotoanassa diaphana carry pedicels either round the posterior half of the ventral surface 

 or only round the hindmost portion of the body. Besides, the size of the lateral 

 pedicels seems to vary considerably in the very same animal. In the family Psychro- 

 potidse the lateral pedicels are nearly of the same size all round the body, while in the 

 two other families it may be affirmed as a rule that the size decreases posteriorly, so that 

 the most posterior pairs become obviously smaller than the anterior or almost rudimentary. 

 Nevertheless, I have found cases, as, for instance, Parelpidia elongata, which form excep- 

 tions to this rule in having the posterior considerably larger than the anterior pedicels. 



The most characteristic mark of the Elasipoda, and that which gives them their 

 symmetrical appearance, is that the pedicels along each side of the ventral surface 

 correspond in number as well as in shape and size, and, being distinctly opposed 

 to one another, constitute pairs. It sometimes happens, however, though rarely, that the 

 number of pedicels on one side exceeds that on the other, but considering that this 

 is the case in one individual while another of the same species has an ecpial number 

 of pedicels along each side, this must be regarded only as an individual peculiarity. 

 But, besides this symmetry in the arrangement of the pedicels, there may often be 

 observed in the different species a tendency in the pedicels to become definite and fixed 

 in number. Numerous individuals of Elpidia glacialis and Scotoplanes globosa having 

 been at my disposal, I have found as a rule that the former species is always provided 

 with four pairs of pedicels and the latter with seven pairs. Unfortunately, I have 

 had only one or two individuals of most species for my examinations ; consequently 

 1 am not able to cite more examples, though I am fully convinced that all forms belonging 

 to the family Elpidiidae possess in common with the two forms above mentioned an 

 almost fixed number of pedicels. Before concluding my account of the pedicels, it is 

 necessary to notice the two forms Oneirophanta mutabilis and Ilyodcemon macidatus in 

 which the pedicels are arranged in a double row along each side. This arrangement in a 



