300 EEPORT OF COMMISSIONER OF FISH AND FISHERIES. 



mandibles are destitute of palpi. The oral opening between the mandi- 

 bles is defended by an upper and lower lip, or labrum and labium, which 

 are, however, median, and not paired organs, like the other parts of the 

 mouth. 



The seven thoracic segments are of firm texture above, but softer 

 underneath. The dorsal surface is in general more or less rounded, and 

 in Cirolana is continued well down at the sides, where, except in the first 

 segment, it is crossed by a suture cutting off a quadrate, or somewhat 

 triangular piece, called an epimeron, or, in the plural, the epimera. The 

 epimera are well shown in the side view of Cirolana concharum (pi. IX, 

 fig. 58). They belong to the legs, and form a portion of the large prox- 

 imal segment called the coxa. Usually, however, the legs are figured 

 as in pi. X, fig. 62 b, without this segment, which adheres strongly to 

 the body; often, as in the first segment of Cirolana, the suture sep- 

 arating it disappears. The remaining six segments of the legs are more 

 slender, and are called respectively, beginning with the segment follow- 

 ing the coxa, the basis, ischium, merus, carpus, propodus, and dactylus, 

 the last being usually slender and curved, often bearing a curved spine 

 or claw at the tip, and, especially in the first pair, capable of flexion on 

 the propodus, so as to form a prehensile hand. In the Tanaidce, as in 

 many of the higher Crustacea, the propodus may be prolonged into a 

 digital process, against which the dactylus closes, forming a chela (pi. 

 XIII, fig. 85), or chelate hand, as in the lobster. In the JEgidm and the 

 Cymothoidw a greater or less number of the dactyli are strongly curved 

 or hooked, for the purpose of retaining firm hold of the host, on which 

 these parasitic species live. Legs thus constructed are called ancoral, as 

 in Livoneca ovalis (pi. XI, fig. 67 d and e). 



Of the seven pairs of legs attached to the thorax or pereion, the first 

 three have in general a resemblance to each other, and are often more 

 or less prehensile, while, as in Chiridotea (pi. IV, figs. 16 and 20), the 

 last four are more strictly locomotive organs; but to this condition 

 of things there are many exceptions, especially in the development of 

 the first pair of legs, which are quite variable throughout the order, be- 

 ing not even pediform in the males of the Gnathiidw, but two-jointed, in 

 our species, and lamelliform (pi. XII, fig. 76 d). Except in this family, 

 however, no confusion arises from speaking of the thoracic appendages 

 as the first to the seventh pair of legs, or thoracic legs, and in general 

 these terms will be used except where it may be necessary to use the 

 technical terms, gnathopods or gnathopoda and pereiopods or pereiopoda, 

 for these organs, as proposed by Spence Bate, according to whose system 

 the first and second pairs are caUed the first and second pairs of 

 gnathopoda* or gnathopods, and the remaining five pairs the first to 

 the fifth pair of pereiopoda or pereiopods. When necessary these 

 terms will be added as explanatory, having the merit of scientific 

 accuracy as well as applicability to other groups of Crustacea, where a 



* See also Edwards, Auu. Sci. uat., Ill, tome xvi, p. 221-291. 



