110 



Fam. 16. Metridiidae. 



Characters. Body of comparatively slender form, with the cephalosome 

 well defined from the 1st pedigerous segment, front somewhat produced and 

 carrying below 2 delicate, ciliated filaments. Last 2 segments of metasome united. 

 Urosorne more or less elongated, and consisting in female of 3, in male of 5 

 segments. Caudal rami comparatively broad, flattened, with the full number of 

 setse. Eye very small, snbventral. Anterior antennae moderately slender, and 

 consisting in female of 24 articulations, the 7th and 8th being united; left antenna 

 in male, as a rule geniculate, and richly supplied with sensory appendages. Posterior 

 antennas and oral parts on the whole normal. The 4 anterior pairs of legs with 

 both rami 3-articulate, outer ramus of 2nd to 4th pairs very large, more or less 

 lamellar, with comparatively short spines, 3 of which occur outside the terminal 

 joint. Inner ramus of 2nd pair with the 1st joint peculiarly transformed. Last 

 pair of legs simple, not natatory, being very small in female, in male, as usual, 

 somewhat larger and prehensile, right leg the larger. No ovisac present in female. 



Remarks. In this new family I propose to include the 2 nearly-allied 

 genera Metridia, Boeck and Pleuromamma, Giesbrecht. These genera, it is true, 

 in some respects apparently exhibit a close resemblance to the Temoridce; but 

 the structure of the natatory legs is essentially different, and more resembles that 

 in the next family (Heterorhabdidce). With this family they also agree in the 

 circumstance that the left anterior antenna in the male is generally prehensile. 

 Finally, a peculiarity, not mentioned in the above diagnosis, may be here named, 

 viz., the luminous power of the animal, when alive. This power seems to be 

 common to all the Metridiidse, whereas it has not been observed in any other 

 Calanoids. In one of the genera (Pleuromamma), a special luminous organ is 

 present, and though this organ is wanting in Metridia, all the species of that 

 genus observed in the living state, have been found to emit light when disturbed. 

 Both genera are represented in the fauna of Norway, and will be treated 

 of below. 



Gen. 18. Metridia, Boeck, 1864. 



Generic Characters. Body slender and elongated, with the anterior divi- 

 sion only slightly tumefied. Cephalosomo without any cervical depression above, 

 rostral projection smooth in front, tentacular filaments very slender. Lateral 



