of the North Atlantic and of North- Western Europe. 627 



many- jointed, geniculated at the base, shortly spiniferous. Mandibles small and 

 weak, palp large. Three pair of limbs posterior to the mandibles, all maxilliform. 

 Palp of the mandibles and first maxillte bearing internally a comb of large setae. 

 First and second maxillae furnished with a large vibratory lamina. Third pair 

 rudimentary in the female, in the male well developed and prehensile. Caudal 

 laminae small and narrow, spiniferous at the extremity. Fam. CytherelUdce, 

 G. 0. Sars, 1865. 



Section II. — Myodocopa. 



Shell ovate, elongated-ovate, or round, sometimes truncate behind, and often 

 produced to less or greater length at the infero-posteal corner, or sometimes at 

 the supero-posteal corner. On the lower portion of the front margin there is 

 usually a sinus for the protrusion of the antennae, and above this the shell is 

 projected in more or less rostrate form. Valves highly calcareous, or thin and 

 almost membranaceous ; surface smooth and polished, or hispid, sometimes 

 reticulated ; at others pitted or roughly sculptm-ed. 



Eyes, usually two, pedunculated, or rudimentary, or even absent in some 

 cases : a central ocellus, except in Conchoeciadoe. Always a frontal tentacle of 

 greater or less length, simple except in Conchceciadce, where it is more develoj^ed, 

 and usually has an expanded, distal, articulated process (capitulum). 



Antennules not adapted for swimming, generally with sensory appendages, 

 which are variously modified, for the most part of considerable size, but small 

 in Conchceciadce. Antennae always consisting of an immensely strong, muscvdar, 

 pyriform or subcordiform basal joint, and a multiarticulate branch, the basal 

 joint of which is long, the rest short, and all, except the first joint, furnished 

 with long annulated setse, which always in ? , and usually in S , are plumose, 

 and form a powerful swimming organ: a secondary branch — usually, but not 

 always, present in ? — when present minute ; in S more developed, and usually 

 (not in Cypridina) formed for grasping, the last of the two or three joints folding 

 back upon the preceding. 



The labrum and labium are little developed ; largest in the Conchceciadce. 

 In Conchceciadce only is the mandible provided with teeth, but is often furnished 

 with a simple or bifid hirsute, or a reflexed falcate process in their place. 

 Attached to the mandible is a 3—4 jointed palp, the first joint of which, in 

 genera provided with the hirsute or falcate process just referred to, is furnished 

 with some peculiarly modified spines: the palp usually ends in one or more 

 ungues, but in Rutiderma a strongly-developed chela takes their place. 



