of the Division Hyperina. 9 



bably fused with the fourth : ultimate pair of pleopoda attached 

 to the latero-posterior margin of the sixth segment. Telson 

 small, round, being not more than one-third the diameter of the 

 sixth segment of the pleon. 



In comparing the young with the parent, we find the differ- 

 ences to be very considerable. The cephalon in the latter is 

 rounded in front, and the walls encroach upon the inferior sur- 

 face, whei'eas in the former it is produced anteriorly to a long 

 point. The pereion of the adult is laterally compressed, and the 

 first two segments are much shorter than the following ; in the 

 young the pereion is not laterally compressed, and all the seg- 

 ments are subequal. The pleon in the young resembles that of 

 the adult, except that the telson, which in the latter is as broad 

 at the base as the preceding segment, in the former is con- 

 siderably narrower. In the adult, the eyes nearly fill the ce- 

 phalon; in the young they are inconspicuous*. The antennae 

 in the adult are obsolete; in the young the anterior pair are 

 largely developed, while the posterior alone are wanting. The 

 organs of the mouth in both the adult and young are of a very 

 rudimentary character. The gnathopoda in both old and young 

 are well developed, but of a very difl'erent formation. In the 

 adult they are developed upon the Hyperine type, a little exag- 

 gerated in feature, but strictly specific in character ; the com- 

 plexly subchelate condition of the organs could not be mistaken 

 for that belonging to any other family ; the carpus is large and 

 inferiorly produced, the extremity forming the process against 

 which the dactylos impinges; whilst the propodos is narrow, 

 and appears to exist as a part of the mobile joint of the 

 chelate organ, and is so described by most authors who have 

 written on the Hyperina. In the young they do not assume the 

 distinctly Hyperine type : although the carpus is inferiorly pro- 

 duced, the propodos is nearly as broad as the carpus, and has 

 the inferior angle produced into a long and strong tooth, against 

 which the dactylos impinges, and not against the inferior angle 

 of the propodos, as is the uniform law in the Hyperina when 

 they impinge at all. The first two pairs of pereiopoda differ 

 only in the relatively imperfect condition of the former, — the 

 small spines on the posterior margin of the carpus and propodos 

 of the adult being wanting in the undeveloped organ, whilst in 

 the latter the dactylos is proportionally much longer than in the 

 former. The third pair of pereiopoda in the young are long and 

 well-developed organs, being only distinguishable from the same 

 in Gammarina by the absence of the squamiform distension of 

 the posterior margin of the basos; whilst those in the adult 



* This may partly arise from the animals having been long dead, and 

 being preserved in spirits. 



1 



