121 



Fam. 3. Pontoporeiidae. 



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

 very tumid. Cephalon not produced anteriorly in the form of a hood. Coxal 

 plates of moderate size, generally fringed with bristles; those of 5th pair 

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

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

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

 sharply deiined. Epistome not at all projecting. Anterior lij) forming a 

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

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

 masticatory part; cutting edge divided into '2 superposed lamelUe; molar 

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

 Maxillse and maxillijieds of usual structure. Gnathojioda comparatively small 

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

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

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

 Branchial lamellte simjjle ; incubatory lamellae slender, fringed at the tip witli 

 long cui'ved setae. Pleopoda as a rule well developed, especially in the male. 

 Uropoda biramous, last pair unlike the preceding pairs in structui'e. Telson 

 flattened, more or less deeply cleft. 



JReniarls. — This family comprises several genera, which on the wliole 

 differ rather markedly from each other, both as to the outer 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 

 h)ose bottom deposit, for which purpose the 3 posterior jiairs of pereiopoda 

 have been more or less peculiarly modified, tlie joints being pai'tly laminarly 

 expanded, and armed with strong spines and l)iistles. The most extreme 

 development in tliis way is found in the genus HaKfloriiis (Lepidactylus), to 

 be desci'ibed in the sequel. Besides the 6 uoi-thern genera recorded in the 

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

 estal)lislied. Tlius Dr. Hansen has added an exclusive arctic genus Prinassiis, 

 and the Hev. Mr. Stebbing descrilies 2 very distinct new genera from the 

 Challenger Expedition, viz., Carchnio and Platjiischnopm, the former being 

 apparently most nearly allied to the genus Bafhyporeia, the latter to tlie 

 genus Hailstorms. 



Cnistatiea. 



