CRUSTACEA MALACOSTRACA. III. 1^5 



Sub-Order Valvifera. 



Of the five families established only two, viz. Idotheidse and Arcturidse, are represented in the 

 material. In large forms of both families I have in vain looked for a prsecoxa and a squama on the 

 antennae, and for a prsecoxa in the maxillipeds. But these mouth-parts differ somewhat in the two 

 sexes, as in ovigerous females the coxa has always a lappet directed backwards evidently in order to 

 produce a current of water to eggs and young. 



When comparing the proximal parts of the maxillipeds of the males of Mesidothea Sabini Kr. 

 (PL XV, fig. 4 a) and Astacilla graniilata G. O. S. (fig. 9 a), both chosen as representatives for the two 

 families, it is seen that in Astacilla we find only the coxa and an undivided epipod (fig. 9 a), the basal 

 part of which is marked off a little by the shape of the margins, while in Mesidothea three pieces are 

 found (fig. 4 a), but a comparison with Astacilla shows that it must be the epipod, which has been 

 divided into a large, transverse basal part (b) and a much larger distal part (d). Comparing the max- 

 illiped of the ovigerous female Mesidothea (fig. 4 b) with that of the male, it is seen that the distal 

 part (d) of the epipod is similar in both sexes, while its basal part (b) and the coxa (/) are much altered. 

 In the female the coxa has its chitinous plate altered in shape, being at the outer side produced into 

 a somewhat short anterior and a very long and very oblique, narrrow posterior lamella; at the inner 

 side of the plate is seen a somewhat narrow and at its basal margin a rather large area of membranous 

 skin, and these membranous parts constitute together a free lappet, which has the margins set with 

 fine hairs. Furthermore the basal part of the epipod has been much enlarged, and its firm chitine is 

 divided into a narrow strip at the coxa and two transverse much larger strips, while all intermediate 

 parts are membranous. — Turning now to Astacilla, we find in the female (fig. 9 b) a somewhat similar 

 structure. The coxa (/) has been produced much backwards as a somewhat long, free lappet; this 

 lappet is well chitinized except along its lateral margins and at the end, where a few hairs are seen. 

 But the epipod [ep\ which is undivided in the male, is in the female divided into a major distal part 

 answering to the male epipod except its most proximal part feebly marked off by the shape of the 

 margins; in the female the proximal part of the epipod has two transverse, chitinized areas with a 

 membranous strip between them, thus moderately similar to the structure in the female Mesidothea. 



In the literature I have found no statement on these differences in the maxillipeds of the two 

 sexes in Idotheidse and Arcturidae, excepting that Sars (Account, p. 87) has a single line on this sexual 

 difference in Astacilla. Recent authors (Sars, Richardson, Stephenseu) generally selected a large spec- 

 imen for the dissection of the mouth-parts; as in Idotheidae adult males are larger than the females, 

 they have generally figured male maxillipeds, and as in Arctums and Astacilla the females are generally 

 much larger than the males, they have, what is really misleading, figured the female maxilliped with 

 its well-sized proximal lappet as type for that limb in the species in question. 



In Arcturus Baffini Sab. the first pair of pleopods have, seen from in front (PL XV, fig. 5 a), 

 three joints in the sympod. First joint, pracoxa (/), is a strongly bent plate of considerable size touch- 

 ing the sternite and the triangular plate representing second joint (2), but it does not touch the prox- 

 imal margin of third joint, while the plate representing second joint is articulated to the third firmly 

 chitinized joint (j) and does not reach the sternite. The intervals between the firm parts are membranous. 



The Ingolf-Expedition. III. 5. 2 4 



