470 CEUSTACEA. 



In the female the posterior antennae are short and rudimentary, 

 while in the adult male they, together with their multiarticulate 

 flagellum, may be as long as the body (as in Nebalia). The upper-lip 

 is usually small, while the deeply cleft under-lip is of considerable 

 size. The mandibles are without palps, and possess a comb of bristles 

 and a powerful masticatory process below their strongly toothed 

 extremity. The anterior maxilla consist of two toothed blades and 

 a cylindrical, flagellate appendage directed backwards. The unpalped 

 maxilla of the second pair is composed of several pairs of masticatory 

 plates lying one above another. The two following pairs of 

 appendages may be distinguished as maxillipeds. The anterior, 

 which corresponds to the palped under-lip of the Isopoda, is five- 

 jointed and may be recognised by the process of the basal joint ; the 

 posterior, which is also usually five-jointed, is of considerable length 

 and the basal joint is cylindrical and elongated. They also bear the 

 large pinnate gill and a peculiar plate. Of the remaining six pairs 

 of thoracic appendages, the two anterior are always formed like the 

 feet of the Schizopoda ; they consist of a six- jointed leg, the basal 

 joint being strongly developed and lamellar, and of a multiarticulate 

 accessory ramus (exopodite) beset with long swimming setae. The 

 four last pairs of appendages are also six- jointed, but are shorter ; 

 they bear in many cases, with the invariable exception of the last 

 pair, a larger or smaller swimming appendage as exopodite. The 

 very narrow and elongated abdomen is, in the female, entirely without 

 swimming feet, but bears on the large sixth segment at the sides of 

 the caudal plate long-stalked biramous caudal styles; while in the 

 male two, three or five pairs of swimming feet may in addition be 

 present on the preceding segments. 



Fam. Diastylidae. Diastylis Rathkii Kr., North Sea. D. Edwardsii Kr. 

 Lcucon nasicus Kr. , Norway. 



(2) Sub-order: Stomatopoda. * 



Elongated Thoracostraca icit/i short cephalo-thoracic shield wJiich 

 does not cover the thoracic segments. There are Jive pair of maxilli- 

 peds and three pair of biramous thoracic feet. The swimming feet on 

 the strongly developed abdomen bear branchial tufts. 



* Besides Dana, M. Edwards and others, compare 0. Fr. Miiller, " Bruch- 

 stuck aus der Entwickelungsgeschichte der Maulfiisser," I. and II., Archiv fur 

 Naturgcxcli., Tom XXVIIL, 1862, and Tom XXIX., 18G3. C. _ Glaus, " Dia 

 Metamorphose der Squilliden," Abliandl. der Oottinger Societat, 1872. C. 

 Grobben, " Die Geschlechtsorgane von Squilla mantis," Sitzungsbcr. der 7i 

 Aliad. der Wtisenssh., Wien, 1876. 



