40 CRUSTACEA. 



these parts are contiguous inferiorly along the internal edge, and 

 form an elongated triangle, the extremity of which is received into 

 two upper cells of the buccal cavity. The tail, which is ample and 

 suborbicular in the females, usually consists of from four to five seg- 

 ments, but never seven. 



Doctor Leach(l) has separated this genus of Fabricius into seve- 

 ral genera, which, however, we will consider as simple divisions. 



Those species which have a transversal shell, with the middle of 

 its sides greatly prolonged or dilated, so as to resemble a cone or 

 cylinder, form his genus Ixa{2). 



Those which have a rhomboidal shell with seven conical points, 

 resembling spines on each side, compose that of Iphis. 



If the shell still has the same rhomboidal figure, but merely pre- 

 sents angles or sinuses on the sides, it becomes his genus Nursia. 



If these lateral edges are smooth, we have his Ebalia. 



The Leucosiae with an ovoid or nearly globular shell, and other- 

 wise distinguished from several of the preceding by the claws being 

 always longer than the body and thicker than the other feet, and by 

 the tarsi being sensibly striate, may be divided thus: 



In some the front projects, or at least is not surpassed by the 

 superior extremity of the buccal cavity. The outer branch of the 

 external foot-jaws is elongated, and almost linear. 



Here the claws are slender, the hands cylindrical, and the fingers 

 long. 



Sometimes the shell is nearly globular, and either very spiny, as 

 in the genus Jlrcania, or smooth as in Ilia. 



At others, the shell is suborbicular and depressed, as in the genus 

 Persephona, or ovoid as in Myra. 



There the claws are thick, with ovoid hands and short fingers. 



They constitute the true Leucosise of that naturalist. 



In the others, the superior extremity of the buccal cavity out- 

 reaches the front. The outer branch of the external foot-jaws is short, 

 and arcuated; the shell rounded and depressed. This last division 

 comprises his genus Phylira. 



Other considerations, founded on the proportions of the feet and 

 the form of the external foot-jaws, strengthen these characters. 



The Leucosie noyau; Ilia nucleus, Leach; Cancer nucleus, Lin., 

 Herbst., XI, 14, is common in the Mediterranean; its shell is 

 globular, granulated on the sides and posteriorly; the front is 

 notched; two teeth on the posterior margin, and two others 



(1) Leach Zool. Misc. Ill; Desmar., Consid. 



(2) Leucosia cylindrus, Fabr., Herbst., 11,2931. 



