121 



Fam. 3. Pontoporeiidse. 



Form of body varying in the different genera, now compressed, now 

 very tumid. Cephalon not produced anteriorly in the form of a hood. ('oxal 

 plates of moderate size, generally fringed with bristles; those of f>th pair 

 bilobed. Metasome generally well developed, with large epimeral plates. 

 Urosome short and stout. Superior antennae, as a rule, shorter than the in- 

 ferior, and furnished with an accessory appendage; joints of the peduncle 

 sharply defined. Epistome not at all projecting. Anterior lip forming a 

 simple rounded prominence; posterior lip quadrilobated, the inner lobes small 

 but well defined. Mandibles comparatively short and thick, with greatly expanded 

 masticatory part; cutting edge divided into 2 superposed lamelhe; molar 

 expansion large and protruding, palp more or less elongate, and 3-articulate. 

 Maxillae and maxillipeds of usual structure. Gnathopoda comparatively small 

 and feeble in structure, generally imperfectly subcheliform or sometimes approach- 

 ing to the chelate form. The 3 posterior pairs of pereiopoda more or less 

 dissimilar in structure and adapted for burrowing in the loose bottom deposit, 

 Branchial lamellae simple; incubatory lamellae slender, fringed at the tip with 

 long curved setae. Pleopoda as a rule well developed, especially in the male. 

 Uropoda biramous, last pair unlike the preceding pairs in structure. Telson 

 flattened, more or less deeply cleft. 



Remarks. This family comprises several genera, which on the whole 

 differ rather markedly from each other, both as to the oiiter habitus and the 

 anatomical structure, so as, perhaps, more properly to be referred to several 

 distinct families. As a characteristic feature common to all the forms under 

 consideration, may be named the great ability of burrowing in the mud or 

 loose bottom deposit, for which purpose the 3 posterior pairs of pereiopoda 

 have been more or less peculiarly modified, the joints being partly lamimu-ly 

 expanded, and armed with strong spines and bristles. The most extreme 

 development in this way is found in the genus Hd-ndoriiix (Lepidactylus), to 

 be described in the sequel. Besides the 6 northern genera recorded in the 

 present work as belonging to this family, a few exotic genera have been 

 established. Thus Dr. Hansen has added an exclusive arctic genus Prinassus, 

 and the Rev. Mr. Stebbing describes 2 very distinct new genera from the 

 Challenger Expedition, viz., Carclmio and Platyischnopns, the former being 

 apparently most nearly allied to the genus Batkyporeia, the latter to the 

 genus Hailstorms. 



16 Crustacea. 



