DR. J. D. MACDONALD ON TANAIS VITTATUS. 69 



The first or basal portions of these limbs form two oval projections beneath the thorax ; 

 the second is a small triangular piece, with which the third is so connected as to present 

 a rounded projection posteriorly, while it extends forwards to articulate with the manus. 

 In the female (figs. 1 & 7) eight or nine stout bristles spring in a row at the outer side 

 of the base of the cutting-border of the manus, while in the male they are interrupted in 

 the middle. Other bristles occur near the articulation, i. e. one on the inner and several 

 on the outer side. 



As already mentioned, the first thoracic ring having coalesced with the head, the six 

 following pairs of legs arise from the six apparent thoracic segments. The first visible 

 segment, distinct from the carapace, must, therefore, carry the second pair of legs. These 

 have long curved thigh-pieces, with which the succeeding joints of the limbs are so arti- 

 culated as to permit them to play their legitimate part as external jaw-feet, curving 

 inwards and forwards round the basal prominence of the first pair. Their claws (fig. 8) 

 are long, simpie, styliform, and but slightly curved ; they are themselves rather longer 

 than the other legs. 



The claws of the third and fourth pairs (figs. 9 & 10) are simply uncinate, while those 

 of the last three pairs (figs. 11, 12, & 13), which are curved forwards, are also combed 

 on either side, though this is not quite so apparent on the inner side in the last pair. 

 Instead of it, however, they present a close row of stiff serrated hairs at the extremity of 

 the penultimate joint, which is moreover roughened with rasping tubercles (13 a), quite 

 like those which beset the whole surface of the body in Limnoria. In all the legs, with 

 the exception of first and second pairs, the third segment presents a row of stout spines on 

 either side of its articulation with the fourth. 



The abdomen consists of five segments, the first three of which bear the respiratory 

 lamellae and swimmerets together. The fourth is much smaller than those preceding it, 

 and without appendage. The fifth is rather more than twice the length of the fourth, 

 broadly shield-shaped, with four rigid hairs projecting backwards from the middle of 

 its posterior border. Besides the swimmerets there is a fourth pair of appendages 

 (figs. 1. 4, 5, & 14), which are rather conspicuous on account of their projection beyond 

 the terminal segment. They have a simple folded lamella on the inner side, and much 

 resemble a pair of three-jointed antennae, with stout diverging hairs at the distal end of 

 each joint. 



The inner ovate and acute leaflets of the abdominal appendages (fig. 4, b) lie flat, and 

 are apparently motionless ; while the outer ones, which are rather semicircular (a), cross 

 over them superficially towards opposite sides. Both borders of the deep leaflets and the 

 outer border of the superficial ones, as well as that of the broad propodia, are beautifully 

 fringed with long flat acute and feathery setae (d). Similar feathery hairs form a trans- 

 verse linear band or fascicle upon the dorsum of the first and second segments. 



The generative pores lie side by side near the middle of the sternal plate, between the 

 two last thoracic limbs. 



The female (fig. 1) carries her eggs in a membraneous expansion or saccule under the 

 thorax ; and, from having observed the chelae and other anatomical characters of the 

 adult in the young soon after leaving the egg, I think it may be concluded that there is 



l 2 



