of the North Atlantic and of North-Western Europe. 681 



■within the dorsal margin ; behind the enclosed space the shell is depressed, and a 

 riblet passes from the infero-posteal corner to the surrounding riblet-wall of the 

 enclosed space. Seen from above, the greatest width is behind the middle and 

 equal to about two-fifths of the length : the form is narrowly- ovate, the anterior 

 extremity wider at its termination than the posterior, which is projected in some- 

 what rostrate form beyond the part which is elevated and enclosed (on the side 

 view) by the bounding riblets. Length, 1-25 mm. ; height, 0-8 mm. 



Antennules in 3 (PI- lui., fig. 12), have the first and second joints sub-equal 

 in length, the former without setse, the latter with one annulated and ciliated seta 

 on the middle of the front margin ; third joint excessively short and rudimentary,* 

 fourth and fifth joints sub-equal, each rather shorter than the second; the 

 former with one proximal and one distal seta on the front margin, a pair of 

 long setse on the middle of the hinder margin, and at its extremity a remark- 

 able appendage, which is another form of the sensory organ of Cypridina. 

 This sensory appendage consists of a short clavate process which is rather longer 

 than wide and has its broadly-rounded extremity covered with a dense brush of 

 filaments of such a length that they extend even beyond the terminal setse of the 

 limb ; rising also from the distal side of the process, but so hidden by the mass 

 of filaments that its base is difficult to detect, is a long annulated seta which 

 stretches forward, side by side with the similar setse of the last joints, sixth joint 

 rudimentary ; termination of limb with four or five long setse, as well as others 

 which are small. 



The antennse have the swimming-branch fiu-nished with nine setse, and its 

 third joint only slightly shorter than the second ; the secondary appendage 

 (fig. 13) is small, but formed for grasping; its basal joint coalescent with the 

 trunk, and indicated only by two minute setse; the second (first free) joint is 

 flexuous, about three times as long as broad, with two short spines, f last joint 

 cylindrical, simple, blunt at the extremity, and reflected on the preceding 

 joint. 



Mandible (fig. 14) without masticating process or peculiar spines, basal joint 

 very stout, first and second joints of palp cmwed, the former the longer, with three 

 or four spinules on the inner margin, and near the extremity of the outer margin 

 two small ringed setse ; second joint with a stout ringed and ciliated seta at the end 

 of the inner margin; third joint with a single long ringed seta on each margin, 

 last joint very minute, terminating in a single, long, gently curved unguis which 

 nearly equals in length the last three joints, and bears a spine point half way 

 down the outer margin ; there are one or two minute spinules by the base of the 



* The limt, vie-wed from one side, appears to have such a joint, hut on the other it is scarcely 

 indicated. 



f "We call them spines, for they are spiniform ; but they seem to have an annulated structure. 



