of the North Atlantic and of North-Western Europe. 



639 



Diagnosis of Genera by the Animal. 



Mandibular palp ending in a single unguis ; penultimate 

 joint shorter tlian antepenultimate, .... 



Mandibular palp ending in more than one unguis, though 

 one sometimes larger than the others ; penultimate 

 joint much longer than antepenultimate. 



Upper tooth of second maxillae narrow, falcate, denti- 

 culated on inner margin. 



Masticating process at base of mandible entire, . 



Masticating process at base of mandible cleft, . 



Upper tooth of second maxillae large, triangular, 



smooth-edged, ....... 



Upper tooth of second maxillse subquadrate, broadly 



truncate at the end, smooth-edged, 

 Upper tooth of second maxillse very large, oblong, 

 with fang-like process at one end, and dentated 

 processes at intervals on its long extremity. 



Nema tohamma. 



Cypridina. 

 Crossophorus. 



Philomedes. 



Tetragonodon. 



Paramekodon. 



N.B. — The animal of Streptoleheris unknown. For the shell see figures of 

 the species. 



COMPAEISON OF THE LiMBS IN THE FAMILIES CyPRIDINID^, RuTIDERMATIDiE, 



AND SaRSIELLID^. 



The eyes consist of a pair, usually well developed in both sexes, but larger 

 in the males, sometimes small or absent in the females, and between these a 

 median ocellus, in front of which is projected a tentacular organ, sometimes 

 short and fusiform as in Cypridina, more commonly elongated and filiform as in 

 Philomedes. 



The antennules (PI. lv., fig. 1) consist of 5-7 joints, and are geniculated at 

 the end of the first joint. The last joint, to which most of the terminal setse are 

 attached, is always very short; the proportionate length of the remaining joint 

 varies in the different genera. At the distal end of the inner margin of the 

 antepenultimate joint is usually attached a conspicuous sensory organ. This 

 organ varies greatly in the different species, and affords good generic character. 

 In Cypridina it is alike in the two sexes (PI. LVa, fig. 3), and in the form of a large, 

 closely-annulated seta, bearing rather short and stiff filaments pinnately arranged 



^ 4X2 



