1894. PROCEEDINGS OF THE NATIONAL MUSEUM. 491 



limbs in wliicli, as in the tliree followino- pairs, the terminal segment 

 (dactylus) closes upon the next segment (manns) like tlie blade of a 

 pen-knife; the last three pairs of thoracic limbs are biramons, having 

 a lateral appendage n])on the penultimate segment, and are adapted 

 for walking; the abdomen is very strongly developed; tutted gills arc 

 carried upon the exopodites of the first five abdominal appendages and 

 the sixth pair (uro])ods), which act with the telson as a powerfid tail 

 fin, are strengthened by a stout i)rocess from the basal segment ending 

 in one or two si^ines. 



Family Squtllid^. 



We may regard the 8fo)naf<)poda as com})rising a single family with 

 the characteristics of the older. For the sake of avoiding circumlocu- 

 tion it has been found desirable to use certain technical expressions. 

 They are. mainly those already used by Brooks, l)ut it may be well at 

 this point to indicatebriefiy their meanings. According to our present 

 morphological ideas the thorax of the Malacostraca consists of eight 

 somites, and those which are usually left uncovered by the carapace in 

 the Squillidte are therefore the fifth, sixth, seventh, and eighth, and 

 sometimes the fourth is also exposed (fig. 13). In the posterior half of 

 the carapace there is often an irregular transverse depression, known 

 as the cervical suture, and there is always besides a pair of longitudinal 

 sutures (pi. xxi). In the geiuis HquiUa there are often five longitudinal 

 carinas upon the carapace — an unpaired median one, an intermediate 

 pair, and a lateral pair. The lateral carinas are often continued into 

 the anterior lateral spines, while the intermediate ones usually extend 

 as marginal carinas around the edges of the posterior lateral lobes 

 (pi. XXT). The eyes are often flattened and have the corneal i)ortion 

 divided into two lobes. In that case there are two principal axes — 

 the peduncular axis («/>, fig, 14), running from the base of the i)cduncle 

 to the line between the lobes, and the corneal axis ((y7, fig. 14), coin- 

 ciding witli the greatest diameter of the corneal portion. The three 

 distal segments of the great raptorial limb are known as the carpus, 

 manus, and dactylus (e, w, and f7, fig. 7). In the higher species of 

 Sqnilla there are eight principal ridges or carina' upon the abdominal 

 somites descril)ed as submedian, intermediate, lateral, and marginal 

 (fig. 0, sc, /c, k; and mc). The seventh abdominal somite, or telson, usu 

 ally has a dorsal median carina, that I shall speak of as the crest, and 

 there is sometimes a ventral one that may be called the keel. The ])ro- 

 jecting points on the margin of the telson fall into two series. The 

 larger ones are the marginal spines, of which there are usually six 

 (figs. 0, 1(», ,sw, im, and /), with sometimes indications of an auditioual 

 l^air (fig. 1(>, al); the smaller ones are the denticles, of which there are 

 six sets (fig. ir>, .sf7, if], and Id). The arrangement of the denticles for 

 each species is often characteristic and may be expressed in a fornuda. 

 The formula for Squilla mantis is 3-4, 1-8, 1; which meaus that in this 



