105 



Group 5. Hyocyprides. 



Remarks. This group appears to be a very sharply defined one, differing, 

 as it does, in some respects rather conspicuously from the other groups here 

 treated of, and on this cause it has indeed by moost recent authors been 

 considered as a distinct subfamily of the Cypridae, Ilyocyprince. I think how- 

 ever that the systematic value of the above named differences has been rather 

 overestimated, and that it might be more appropriate to regard it as merely 

 a subsection of the subfamily Cyprinae, as here defined. The group as yet 

 only comprises 2 closely related genera, both of which are represented in the 

 Fauna of Norway. 



Gen. 16. Ilyocypris, Brady & Norm. 1889. 



Generic Characters. Shell of rather firm consistency, more or less oblong 

 quadrangular in shape, with the anterior part of the dorsal face compressed 

 and exhibiting on each side 2 successive vertical folds, the posterior part some- 

 what flattened along the middle; surface of valves sculptured with numerous 

 closely set pits, edges highly chitinised and finely denticulate, but without any 

 pellucid border. Eye small, simple. Antennae adapted for swimming, the 

 natatory setae in both pairs very long and slender. Mandibles of normal 

 structure. Maxillae with the masticatory lobes short and stout, none of the 

 spines on the outermost lobe remarkably strong, palp of moderate size, with 

 the distal joint short and broad, sub-spatulate in shape. Maxillipeds with a 

 well defined vibratory plate at the base, palp in female very small, but distinctly 

 biarticulate; palps in male, as usual, transformed and nearly symmetrical, both 

 unusually slender and narrow, with the propodus not at all dilated and the 

 dactylus rather feeble. Anterior legs of moderate size, with the penultimate 

 and antepenultimate joints, as a rule, confluent. Posterior legs comparatively 

 short and generally bent in a zigzag manner, penultimate joint undivided and 

 provided inside with 2 slender setae, terminal joint somewhat conical in shape, 

 and carrying 3 well defined setae, 2 of which issue from the tip, the 3rd from 

 the outer edge of the joint. Caudal rami comparatively small, but built in 

 the usual manner. Copulative appendages of male terminating in 2 unequal 

 lappets, the lower one narrow cylindrical in shape, the upper rather produced 

 and securiform expanded at the end. Ejaculatory tubes slender, with about 

 20 well defined whorls of radiating spikes, number of spikes in each whorl 

 rather small; proximal end of the tubes somewhat bulbously produced. 



13 Crustacea. 



