I. '08. . 14 



The absence of podobranchs in Amalopenaeus is not merely 

 a feature of immaturity, for specimens of 40 mm. in length 

 show no trace of them, while the petasma and thelycum are 

 well developed in examples little more than half this length. 



Several recent authors regard Amalopenaeus as a synonym 

 of Gennadas and, even when describing new species, omit all 

 reference to this question of the podobranchs. The presence 

 or absence of these gills is, however, acknowledged to be of 

 great importance in separating the genera of Penaeidae (see 

 Alcock, 1901, p. 12), so that although no other valid distinc- 

 tions can be given it seems best to retain the two genera as 

 distinct. The absence of podobranchs in Amalopenaeus is a 

 factor of considerable importance in the study of the evolution 

 of this and of the allied genera, for in this respect Amalo- 

 penaeus is more highly specialized than Gennadas, which 

 forms an intermediate link between it and the still more primi- 

 tive Benthesicymus (see Bouvier, 1906, pp. 9-13). 



Amalopenaeus elegans,^ Smith. 



PI. I, Figs. 1-16. 



Amalopenaeus elegans, Smith, 1882, PL xiv, figs. 8-14; 

 PI. XV, figs. 1-5. 

 Gennadas elegans, Bouvier, 1908, PI. vii {uhi syn.). 



Bouvier (1908) has already given a long and complete de- 

 scription of this species ; it will suffice here to mention the 

 characters which separate it from allied forms. 



The distance between the cervical and post-cervical grooves, 

 measured dorsally, is not more than one-sixth of the distance 

 from the latter groove to the hinder margin of the carapace. 

 The antennary angle is acute and prominent ; the infra-anten- 

 nary angle is also acute, but is bluntly rounded at its apex. A 

 small branchiostegal spine is present. The second joint of the 

 antennular peduncle, measured dorsally, is only half the length 

 of the ultimate joint. The antenna! scale is three times as 

 long as wide and the convex outer margin terminates in a 

 very small spine, which does not extend as far foi'wards as the 

 lamella. 



The second joint of the mandibular palp (fig. 7) is about as 

 long as the width of the basal joint. In the second maxilla 

 (fig. 5) the anterior lobe of the internal lacinia is strongly 

 contracted behind its apex. The chelae of the second pair 

 of pereiopods are shorter than the carpus, while in the third 

 pair the merus is distinctly longer than the carpus. 



1 My statement (1906, 2) that A. elegans is a synonym of Gennadas 

 parvus, Sp. Bate, I now regard as erroneous. In a paper on the Chal- 

 lenger species of Gennadas, published recently (1909) I have given fresh 

 descriptions and figures of Spence Bate's types. 



