2b''2 CRUSTACEA. 



two feet; the first ten, with the exception of the two anterior ones in the 

 mules, are terminated by a didactyle forceps, and inserted, as well 

 as the two that follow, under a large semi-lunar shield ; the latter 

 have the sexual organs attached to them, and the form of large 

 leaflets, as in the case with the ten following, which are branchial 

 and inserted under a second shell, terminated by a very hard, ensiform 

 and moveable stylet. They are wandering animals, and form the 

 genus , 



LIMULUS, Fab. 



The species are known in commerce by the name of the Molucca 

 Crab. The suborbicular, slightly elongated, and posteriorly narrowed 

 body is divided into two parts, invested by a solid shell composed of 

 two pieces, one to each part, very hollow beneath, and presenting 

 above two longitudinal sulci, one on each side, and a carina on the 

 middle of the back. The first part of the shell, or that which covers 

 the fore-part of the body, is much larger than the other, forms an 

 extensive semi-lunar shield, with a reflected edge, furnished above 

 with two oval eyes of numerous facets, resembling granules, one on 

 each side, exterior to a longitudinal carina; and on the anterior ex- 

 tremity of the middle one, and common to both pieces of the shell, 

 two small, closely approximated, simple eyes*; these carinse are 

 armed with teeth or acute tubercles. The duplicature of this shell 

 at its anterior extremity, beneath, forms a level border, strongly 

 arcuated, and terminated inferiorly by a double arc, projecting like 

 a tooth towards the centre of union . Immediately under this projec- 

 tion, in the cavity of the shield, is a small inflated labrum, carinated 

 in the middle, and terminating in a point, above which are inserted 

 two little antennae, in the form of small didactyle forceps, flexed into 

 an elbow in the middle of their length, at the point of union between 

 the first joint and the second, or of the forceps properly so styled. 

 Directly beneath, inserted and approximated by pairs, and on two 

 lines, are twelve feet, the ten first of which, the two or four anterior 

 ones of the males excepted, terminate in a didactyle forceps ; their 

 radical joint, projecting inwards like a lobe and covered with points, 

 performs the office of a jaw. The size of these feet augments pro- 

 gressively ; those of the fifth pair excepted, they are all composed of 

 six joints, the moveable toe of the forceps included. The latter have 

 an additional joint, and also differ from the preceding ones by having, 

 at their external base, a bi-articulated appendage, directed back- 

 wards, the last joint of which is compressed and obtuse ; by their 

 fifth joint being terminated on the inner side by five small, moveable, 

 horny, narrow, elongated and pointed leaflets, and by the two toes 

 of the forceps being moveable or articulated at base. The two pieces 

 situated between these feet, which M. Savigny considers as the 

 ligula, appear to me to be merely two maxillary lobes of these 

 organs, but detached or free. The pharynx occupies the interval 

 included by all these feet. The males are distinguished from the 



* One on each side of the tooth that terminates this carina. 



