248 t^P"'' 



After examining, as well as I can without the aid of dissection, the 

 larger species of SqnduJum here described, I feel little hesitation in 

 stating my opinion that the abdomen in Sepidulum will be found to be 

 composed of six horny ventral plates, and similar in structure and 

 functional value to the abdomen of Amphiops, viz., a basal segment 

 placed in a vertical direction immediately behind the coxa?, so as to be 

 quite invisible except on dissection, a second segment reduced in size 

 to an extremely narrow band, which is placed at right angles to the 

 basal segment, and four large apical glabrous segments ; whereas in 

 Sperchens emarginatus the live apical segments are each about equally 

 developed and are pubescent, the basal segment being glabrous and 

 similar in form and position to that of Sepidulum. The difference then 

 in structure of the abdomen in SpercJieus emarginatus and Sepkluhim 

 will, I believe, be found to consist in the great reduction in size of the 

 2nd horny segment in Sepidulum, and in the apical segments being 

 glabrous and therefore unfitted for detaining air for respiratory 

 purposes. Precisely in these points the Spercheus from Australia here 

 described stands intermediate ; in it the four apical segments are large 

 and glabrous, while the segment immediately behind the coxa? is pu- 

 bescent, but its surface is about half cut away on each side in adaptation 

 to the coxjB. 



The characters furnished by the legs and abdomen seem to me 

 therefore to indicate rather the affinity of Sepidulum with Spej^cJieus 

 than the contrary. On the other hand, the antennae remain very 

 different in the two genera, the structure in Sepidulum shewing no 

 approach to the peculiar structure of these organs in Spercheus. 



It is important to recall that Spercheus carries its eggs in a sac about 

 with it, the sac being placed on the under surface of the hind-body ; the 

 structure of the abdomen, and the ample elytra (when the sac is 

 attached and retained in position by the coxae and femora), allowing it 

 to find complete protection. Sepidulum costatum also carries and 

 protects its eggs in a similar manner : not only does the structure of 

 the abdomen indicate this, but I have direct evidence of the fact, 

 inasmuch as one of the two specimens sent me by Dr. Leconte had, 

 when it reached me, its egg sac still attached and containing a few ova. 



The modifications of structure of the ventral segments in the 

 group SijdropliilidcB are of singular interest to the student, being 

 controlled as they are by three, if not more, important functional 

 relations ; viz. : relations to respiratory needs of aquatic life ; 2nd, 

 protection of eggs by their being carried about by the female ; and 



