334 MR. A. y. JENNINGS ON TUE STRUCTURE OF 



form a brood-pouch,"* — even if they apply to other Isopoda, are 

 not applicable to tliis genus. 



The second pair of oostegites rise from a calcification prolonged 

 down from the anterior region of the thickening over the second 

 limb-socket. They overlap in front the bases of the first pair, 

 and are, in turn, overlapped by the third oostegites. These rise 

 in a similar manner from a descending calcification in front of 

 the third thoracic limb-socket, and they overlap the fourth pair 

 of plates behind as well as the second in front. 



Tlhe fourth oostegites are the largest pair, and seem to be con- 

 nected with the sockets of both the fourth and fifth pairs of 

 limbs : the calcareous supporting bar derived from both these 

 sources takes a semicircular sweep backward toward the postero- 

 dorsal angle. 



The fifth oostegites rise from in front of the sixth pair of 

 limbs. They overlap the fourth pair in front, and are prolonged 

 backward as a pair of oblong plates covering the abdominal 

 appendages for more than half the length of that region of the 

 body, and by pressing on the large first abdominal appendages 

 completely close the brood-cliamber behind. 



These four pairs of plates form by far the greater part of the 

 wall of the brood-chamber ; but between the anterior margins 

 of the second pair and the sternal region of the head the space 

 is filled in by the small first pair, which fit closely against the 

 second oostegites behind and are appressed to the maxillipedes 

 above, thus entirely closing the chamber in front, just as the 

 fifth oostegites close it behind. 



III. The Abdominal Region and its Appendages. 



The third region of the body consists of six abdominal segments 

 and a broad triangular caudal plate, the segments being fused 

 together, as already stated and as implied by the generic name. 



Viewed dorsally, this area still shows the lines of suture of the 

 various segments, and the central part is distinctly marked off 

 from the lateral, giving an appearance much like that of a 

 trilobite pygidium. The caudal plate is thin and delicate in 

 structure, mnrked by light and dark bands like those on the 

 abdominal appendages — a similarity which suggests that it may 

 serve (and the oostegites also) as an accessory respiratory organ. 



* ' Text-book of Zoology,' Claus-Sedgwick, 1884, p. 457. Other cases might 

 be added ; and Milne Edwards, in the original description, refers to the limbs 

 " carrying at their bases large foliaceous plates." 



