4.5 L' CRUSTACEA. 



This extraordinary genus has been consiilered as affording proof of the relation of the Trilobites to the Isopodous 

 Crustacea, the body being divided into three longitudinal portions, as in those fossils. The genus has lately been 

 described and figured in detail by Eights, under the name oi Brongniartia Trilobltoides, in the Transactions of the 

 Albany Institute.'] 



In the other Cymothoada the eyes are lateral, and not placed upon tubercles, and the tail is composed of four or 

 six joints; of these the majority have the eyes not formed of granular ocelli; the antenn.ne are at least seven- 

 jointed, and the six fore-legs terminated by a strong hook ; of these the following subgenera have the tail always 

 six-jointed, and the lower antennie never exceed in length half of the body. 



Cymotlwa, Fab., having the mandibles not exposed, the antennae of nearly equal length, the eyes slightly appa- 

 rent, and the terminal joint of the tail transverse-quadrate. Type, Cymothoa Qistruni, Fab. [These animals were 

 well known to the ancients, who gave them the name of CEstrus and Asilus, from the resemblance between their 

 habits and those of the breeze-flies. Aristotle says of the species above mentioned, " Fishes are attacked by a 

 sea-louse, which is not produced from the fish but from the mud."] 



IcMhyophilus, Latr. (NerocilaaxiA Lironeca, Leach,) difters from the last in having the terminal segment of the 

 tail nearly triangular. To these succeed various subgenera, instituted by Leach upon structural characters, such 

 as the relative length of the antennas, form of the swimming plates of the tail, &c. 



In CEffa, and several others, the eyes are generally large, and converge anteriorly. 



Synodns, Latr., having also six segments to the tail, ditTers from all the preceding in tne large size of its 

 exserted mandibles. 



Ciroluna, Leach, and several others, have only five segments in the tail, and the length of the inferior antennse 

 is greater than that of half the body. 



Ewydice, Leach, belonging to this division, naturally conducts us in the granular structure of its eyes to 



Limnoria, Leach, in which these organs resemble numerous ocelli, placed close together, which have the antenna 

 inserted in a line, and not composed of more than four joints, and all the legs are formed for walking. The tail is 6- 

 jointed, the terminal joint being large and suborbicular. The only known (recent) species is the L. terebrans, Leach, 

 which, although not more than a sixth of an inch in length, is, in its powers of multiplication, exceedingly destruc- 

 tive. It pierces the wood of vessels in different directions with astonishing alacrity, and contracts itself mto a 

 ball when alarmed. It is found in diflferent parts of the British Ocean, [attacking piles of wood immersed in the 

 water in our dockyards, flood-gates, timber-bridges, chain-piers, &c., and which it perforates in a most alarming 

 manner. The boring of the insect having for its object the procuring of food, the contents of its stomach resem- 

 ble comminuted wood. It is necessary that the hole in which it is at work should be filled with salt water. 

 Coating the wood with copper-headed nails, and the use of Kyanized wood, have been suggested as remedies against 

 its attacks]. 



Professor Germar forwarded to Dejean the figure and description of a small fossil crustaceoiis animal, which 

 appears to us to belong to this subgenus. 



The third section, Sph^romides, Latr., cxliibits four distinct and setaceous or conical antcnnjE, ter- 

 minated (except in Anthura) by a multiarticulate filament : the lower pair is always the longest, and 

 inserted beneath the basal joint of the upper, which is thick and broad. The mouth is of the ordinary 

 form. The braiichiaj are vesicular or soft, naked, and disposed longitudinally in pairs. The tail is only 

 composed of two complete and moveable segments, the first of which, however, exhibits impressed 

 and transverse lines, indicating the vestiges of the same number of segments. On each side of the pos- 

 terior extremity of the body is a swimmeret, terminated by two plates, of which the inferior alone is 

 moveable, and the upper is formed by an external elongation of the common support. The branchial 

 appendages are curved inwards ; the inner side of the anterior pair is accompanied in the males with a 

 small linear and elongated piece. The anterior part of the head, situated beneath the antennas, is 

 triangular, or in the shape of a heart reversed. The majority have the body oval or oblong, assuming 

 the form of a ball when contracted. 



Zuzara, Leach (with very large swimmerets), and Sph<eroma, Latr. (with moderate sized-swimmerets), have the 

 impressed lines on the basal segments of the tail not extended to the sides. In the following they extend to the 

 margin, forming as many incisions, and the basal joint of the antennae forms a long square or linear plate. 



Na'sa and Campecopiea, Leach, have the sixth segment of the body considerably longer than the preceding, 

 whilst it is of equal size in 



Ciliccca, Leach, Cymodocea, Leach, and Dynamene, Leach, distinguished by variations in the form of the 

 swimmeret and the sixth segment of the body. 



Anthura, Leach, differs from all the preceding in its vermiform body, and in having the antenna; scarcely as 

 long as the head, and 4-jointed. The plates of the swimmeret form a kind of capsule. (Oniscus gracilis, Mon- 

 tague.) 



In the fourth section, Idoteides, Leach, the antennae are also four in number, but placed in the 

 same transverse and horizontal line ; the lateral ones are terminated l)y a multiarticulate and gradually 

 attenuated filament, the intermediate short, filiform, or slightly thickened at the tip, and 4-jointed, 

 none of the joints being articulated. The mouth is composed of the same parts as in the preceding. 



