DECAPODA. 475 



Fam. Euphausidae. Euphuiiiin. xpli-nden* Dana, Atl. Ocean. Thysanopoda 

 Fam. Lophogastridae. Loplunjaxter typicnx Sars, Norway. 



(4) Sub-order : Decapoda.* 



Podophtlmlniia with large dorsal cephalo-thoracic shield, ivhich is 

 usually fused with all the segments of the head and tl>r<i.<-. They 

 have three (two) pairs of masdllipeds and ten (twelve) ambulatory 

 limbs, some of ivhich are armed with chelce. 



The head and thorax are completely covered by the dorsal carapace, 

 the lateral expansions of which cover the basal joints of the maxil- 

 lipeds and legs, forming a branchial chamber on either side, in which 

 the gills are concealed. Only the last thoracic segment may retain 

 its independence and be more or less movable. The shell is pro- 

 longed into a frontal spine (the rostrum) between the eyes. The 

 firm, calcified integument of the dorsal carapace presents, especially 

 in the larger forms, symmetrical prominences caused by the sub- 

 jacent internal organs : these may be distinguished as regions and 

 named in accordance with the internal organs. 



The abdomen presents considerable differences both of size and 

 form throughout the sub-order. In the Macrura it is of considerable, 

 size, possesses a hard exoskeleton, and, in addition to the five pairs of 

 feet of which the anterior are' often aborted in the female, is 

 provided with a large swimming fin (the telson and the pair of 

 large swimming feet of the sixth segment). In the Brachyura the 

 abdomen is without a caudal fin and is reduced to a broad (female) 

 or a narrow triangular (male) plate, which is bent up against the 

 concave sternal surface of the thorax. The abdominal feet also are 

 slender and styliform, and in the male are only developed on the two 

 anterior segments. 



Appendages. The anterior antennae in the Brachyura are often 

 concealed in lateral pits; they usually arise beneath the movably 

 articulated eye-stalks, and consist of a three-jointed basal portion 

 bearing two or three multiarticulate flagella. The posterior antennae 



* Herbst. " Versuch einer Naturgeschichte der Krabben mid Krebse," H 

 Bde., Berlin, 1782-1804. Leach. ' Malacostraca podophthalma Britannia-,'' 

 London 1817 to 1821. Th. Bell. " A history of the British stalkeyed Crustacea." 

 London, 1853. H. Rathki-, " Untersuchungen liber die Bildung uml Entwick- 

 elung des Flusskrebses," Leipzig, 1829. Spence Bate, "On the development 

 of Decapod Crustacea," Phil. Trans. <>f tin- Roy. Sue., London, 185',). C. Clans. 

 ' Zur Kenntniss der Malaccstrakenlarven," Wurzb. natum-isx. Zc itx<- In-., Tom 

 II., 1861. Fr. Miiller, "Die Verwandluny der Garneelen," Arch if fiir 

 ft., Tom XIX.. 1863. Fr. Miiller, "Fiir Darwin," Leipzig, 1861. 



