56 ON THE CARAPAX AND STERNUM 



of the antennae, the antennules have their insertion at the 

 anterior end of this plate instead of at the sides as would 

 normally be the case. A narrow extension of the main 

 (fold) plate separates the basal joint of the appendages. 

 In Homarus this sternum is moderately developed and 

 occupies its normal position. There is no indication 

 among the Macroura or the Brachyura, of the existence of 

 any other parts of the typical somite in either of these 

 two segments. 



Antennary and mandibulary somites. As re- 

 gards the sterna of the third and fourth somites in Chlo- 

 rodius and Scylla, I cannot do better than refer to Dana's 

 admirable description (loc. cit., pp. 24-28). This des- 

 cription of Chlorodius will apply in every particular to 

 Actceodes, figs. 4, 6 and 7. In Cancer and Platyonichus 

 the facial region is too much fused to admit of any accur- 

 ate distinction of the parts. In Palinurus the antennary 

 sternum is greatly enlarged and forms the lower part of 

 the nasal projection. At its upper termination it furnishes 

 the basal portion of the antennulary sockets : from this 

 point it spreads out rapidly and extends entirely across the 

 ventral surface of the body forming the anterior, lower 

 one-third of the boundary of each antennary socket. The 

 openings of the green glands are near to its outer angle, 

 on the suture separating it from the mandibulary sternum. 

 Its connections with the anterior half or cephalic portion 

 of the carapax are very distinct and in the form of a beaded 

 suture. The mandibular sternum is separated from the 

 episternal pieces by a short suture, these latter in turn are 

 separated from the epimerals by a suture passing backward 

 and inward toward the median ventral line. In Lithodes, 

 figs. 11 and 13, and Homarus, figs. 5 and 17, the epister- 

 nals and epimerals of both antennary and mandibulary 

 somites are present and consequently one is able to 



