On the Distribution of the Rhabdophora. 273 



are small and rudimentary ; but there is a very large and ter- 

 minally bilobed lamella, apparently representing the exognath, 

 which extends forward considerably fj 



in front of the epistome, where its 

 terminal lobes are somewhat upturned 

 and serve as the lower wall of a tube 

 from the efferent branchial opening. Terminal portion of the 

 This lamella is continuous posteriorly second pereiopod of the 

 with the very large epignath, which ng slcle ' 

 extends far back into the branchial chamber. 



The fifth, or last, pair of pereiopods are considerably shorter 

 and more slender than the fourth, and subchelate (fig. 4) . 



The first pleopods have an 



imperfect articulation about a ^ ^ Eg;4 - 



third of the way from the base tf -^ ■-'-----■ 

 to the tip; the basal portion is r ~ && 



somewhat triquetral; and the Terminal portion of the fifth 

 terminal portion expands into pereiopod of the left side. 

 a smooth, naked, and thin 



lanceolate lamella slightly concave posteriorly. The second 

 pleopods are similar to the succeeding pairs, not greatly modi- 

 fied as in Astacus and its near allies. The lamella? are nar- 

 row, lanceolate, and nearly equal in size ; and the inner 

 lamella bears the two small styliform processes usually cha- 

 racteristic of males among Macrura. The three succeeding 

 pairs of pleopods are similar to those of the second pair ; but, 

 as usual, they all want the outer of the two styliform processes 

 on the inner margin of the inner lamellae. 



New Haven, Conn., U. S. A., 

 Feb. 11, 1880. 



XXVII. — On the Geological Distribution of the Rhabdophora. 

 By Chaeles Lapwoeth, F.G.S. &c. 



Part III. Results. 



[Continued from p. 62.] 



(a) Geological. — The conclusions which may be drawn from 

 the data now before us, as detailed in the preceding pages, 

 arrange themselves very naturally under two distinct heads. 

 In the first place, we shall consider the various forms of 

 Rhabdophora there enumerated from the geological or strati- 

 graphical point of view, treating of the several groups and 

 individuals as possible indices of the systematic place of their 



