No. VII. CRUSTACEA 251 



A towing-net gathering from Baffin's Bay, lat. 73° 33' N., 

 long. 76° 59' W., made September 16, 1876, the water at the 

 temperature of 34°*4, contains numerous specimens of 

 Metridina (Metridia) armata, Boeck. 1 This species has 

 been described by Professor Brady from the Irish coast under 

 the name of Paracalanus hibernicus, 2 and I am indebted to 

 him for the opportunity of comparing these Irish specimens 

 (since synonymised by him with Boeck's genus) with those 

 of the Arctic Sea. They agree in every respect except per- 

 haps that the terminal spines of the swimming feet are 

 longer in proportion to the joint from which they spring 

 in the Arctic than they are in specimens from the warmer 

 seas. With respect to size we find here, as in so many 

 other instances among the Invertebrata, an extraordinary 

 development of the Arctic specimens, which are at least six 

 times the size of those from the Irish coast, and measure 

 five millimetres in length, exclusive of the antennae. It is 

 quite possible that this genus may prove to be synonymous 

 with Pleuromma of Claus ; but if that be so, the mature male 

 of Metridina armata has not yet been observed, and the 

 males which Professor Brady and myself have examined must 

 be considered as immature, and not yet to have attained the 

 full development of those limbs which specially characterise 

 the male sex. Claus has named his genus ' Pleuromma ' 

 to indicate the presence of an eye, which he describes and 

 figures as situated ' penes maxillipedum posticorum basin.' 

 It is not a little remarkable that, attached to the maxillipecl 

 of one of the specimens of Metridina armata procured by 

 Dr. Moss, is a group of parasitic organisms, each of which 

 is in the form of a little globular body supported on a pedicel 

 of greater or less length. Sufficient cannot be made out of 

 the organic structure of these parasites to determine the 

 class of animals to which they should be referred. They are 



1 Boeck's genus is Metridia. I have slightly changed the termination 

 to Metridina in order to avoid confusion with Metridium of Oken, of 

 which our well-known sea-anemone {Aetinoloba dianthus) is the type. 

 Ann. Nat. Hist.; S. iv. Vol. xii. p. 126, PI. viii. fig. 1-3. 



2 i 



