86 AN ACCOUNT OP TWO NEW CRUSTACEA 



pound eyes of insects. Its body is composed of several plates fold- 

 ing over each other, which, like the joints of the Lobster's tail, 

 admit of considerable motion. They are prolonged laterally, so as 

 to form a serrated edge to the body on each side. Its legs corres- 

 pond to the number of the plates, at least of the projecting ones ; 

 and beneath the tail are a number of fringed appendages, which 

 perform the office of gills. The Scrolls is found on both shores of 

 the Atlantic. 



The next genus, Limulus, or King-crab (ibid., pi. 45, fig. 1), 

 usually wants the antennae, dorsal plates, and ribs of the Serolis ; 

 Its body is formed of a shield, consisting of two plates jointed trans- 

 versely — the anterior semi-circular, the posterior triangular and ter- 

 minated by a pointed tail, and its edges serrated and set with six 

 spines on each side. It has four eyes — two compound close to the 

 division of the shield, and two simple eyes, lying more in front, 

 close to the median line. Its antennae are very small ; but it has 

 twelve legs, and ten paddle gills. Its habitation is confined to the 

 warm seas of India and America. 



The third genus, Branchi'pus (ibid., pi. 45, fig. 4), is the ani- 

 mal with which many persons are familiar from its exhibition in the 

 solar microscope, where its agility, voracity, and the extraordinary 

 vibrations of its paddles and tail, while the body was at rest, were 

 remarkably striking. It has no proper feet or legs, but its mem- 

 bers, and even its tail, being fringed with gills, answer the pur- 

 poses of organs of locomotion and respiration. It possesses antennae, 

 and inhabits fresh water. 



Lastly, the Trilobite, (see plate, fig. 1), imperfect as it has 

 hitherto been found, presents some of the characters of the two for- 

 mer geneia, and, according to Brongniart, there is great reason to 

 believe, of the latter also. Thus, it has the jointed body of the 

 Serolis, and the large anterior plate or shield of the Limulus, and 

 in some species the tail ; but it has neither antennee, legs, nor gills, 

 though M. Brongniart conceives that it did possess the paddle gills 

 of the Branchipus. Mr. Parkinson also believes that he has detect- 

 ed the existence of legs in one specimen, and M. Goldfuss gives 

 some sections of a Calymene in which not only the presence of a 

 ventral as well as a dorsal plate is clearly established, but also that 

 of certain members, but whether these are legs or paddle-gills is not 

 so evident. This account in vol. xv. of the Ann. des Sc. Nat., seems 

 to have escaped the attention of English geologists, for Dr. Buck- 

 land says decidedly, that no Trilobitehas been found possessed of legs 

 or antennfe. All these classes of animals are aquatic. 



