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CHISMOBRANCHIAT A CHITON. 



matists where to place them. The characters are : 

 the head round, blunt at the muzzle, distinguished 

 from the body by a simple fold, and covered with 

 polygonal scales, which are large for the size of the 

 animal but few in number ; the nostrils and eyes are 

 not very conspicuous ; the jaws are of nearly equal 

 length ; the body is long, cylindrical, covered with 

 rather large four-sided scales, which are similar both 

 on the back and the belly, and are verticillate or 

 placed in whirls round the body ; there are only two 

 feet which are very near the head, well developed, 

 and each containing five toes with distinct claws ; 

 and the tail is blunt. 



There is only one species, C. Mexicanut, which is 

 about eight or ten inches long, and as thick as the 

 little finger. It is marked with about two hundred 

 and twenty rings of scales, which form a half ring on 

 the upper part of the body, and another on the under, 

 meeting each other at two lateral lines, which are 

 very straight and very definite. There are two lines 

 of pores on the under part of the body ; the tongue 

 is a little extensible, and terminates in two small 

 horny points ; its ears are covered with the skin, and 

 consequently not visible externally. It is of a flesh 

 colour, and in this, in its general appearance, and its 

 being possessed of only one large lung, it approaches 

 in character to amphisbo3na among the serpents, but 

 in its skeleton it is very different. The bones of its 

 two feet are well developed, having distinct blade- 

 bones, and being supported by clavicles butting 

 against a small sternum. Thus it can use its two 

 feet with great dexterity in walking, in climbing, and 

 in grasping. Altogether this is one of the most sin- 

 gular animals with which we are acquainted, and the 

 different parts of its organisation would lead to the 

 placing of it in very different parts of the system. 

 The bones are understood, though this point has not 

 been very well ascertained, to resemble, m their gene- 

 ral texture, the bones of warm-blooded animals more 

 than those of reptiles, while the general external cha- 

 racters bear at least some resemblance to those of the 

 lizards, and respiratory system to that of the serpents. 

 This animal is understood to be entirely insectivorous, 

 and it is perfectly innocuous. 



CHISMOBRANCHIATA (Blainville). Second 

 order of the second class of molluscs, Paracephalo- 

 phora. The animals of this order possess aquatic 

 organs of respiration, branchial or pectinated, placed 

 at the anterior part of the back, in a large cavity, 

 communicating with the ambient fluid by a large 

 oblique, anterior slit. Mouth without teeth, but the 

 lower part furnished with a lingual muscle ; some are 

 without shells, some are interior or external, very 

 flat, aperture very large, entire, and without a colu- 

 mella. This order includes the genera Coriocella, 

 Sigaretus, Cryptostoma, Oxinoe, Soumatella, and Vc- 

 lutina. The order is composed of shells, all of which 

 are marine, and the animal probably herbivorous. 



CHITON (Linnaeus, Cuvier, &c.) This singular 

 mollusc has undergone no change by the arrangement 

 of modern naturalists; its characters are so well 

 defined, and possess so few variations, that it cannot 

 by any possible chance become blended with other 

 genera. It is a genus perfectly distinct from all 

 other of the animal series ; they seem to form the 

 transition from molluscs to insects. The separation 

 of this genus into small natural groups is attended 

 with much difficulty ; it may, however, be ultimately 

 accomplished by careful study of the animal and its 



covering. The only certain guide hitherto pursued, 

 are the sides of the valves, and the number of tooth- 

 like processes each presents, when detached from 

 the membranous substance which surrounds them ; the 

 striae, granulations, punctures, and other external 

 markings, also assist in classing the species. Lamarck 

 observes respecting this well known but singular 

 mollusc, that it seems more like an univalve than a 

 multivalve, and should only be considered an elon- . 

 gated shell, with the testaceous portions of it trans- 

 versely broken by nature, at its first formation, into 

 a number of distinct moveable parts, in order to faci- 

 litate the animal's motion. These valves or testaceous 

 portions may be considered never to vary in charac- 

 teristic marks, beyond eight in number, though 

 instances have been met with of specimens with only 

 seven. These are inserted at the lateral extremities 

 by certain toothed processes above alluded to, into a 

 tough ligament surrounding the outer margin, firmly 

 uniting them together in their proper position ; this 

 ligament is sometimes fleshy, coriaceous, smooth, 

 wrinkled, covered with scales, or beset with tufts of 

 hair ; and in one species Chiton spinosus, it has nume- 

 rous tubular, slightly curved, long thin black spines ; 

 a tough internal membrane connects the under part 

 of the valves or portions, allowing the animal to con- 

 tract its shell in a globular form or fully to expand it. 

 When these valves are all united on the animal's 

 back, they form an elliptical shell, the centre part of 

 which is more elevated than the rest; the valves 

 slightly overlap each other, and each succeeding one 

 is less convex towards the margin. One species has 

 callous adhesions longitudinally placed on the back 

 of the valves; some are elegantly marked by the 

 arrangement of their striae, granulations, &c. The 

 interior of the valves is generally white, but some are 

 green, and one species a bright rose-colour; they 

 adhere to rocks covered by the sea, to the backs of 

 tortoises, fishes, or other marine objects, and so fast 

 do they retain their position by exhausting the air 

 beneath their bodies, that it requires a strong lever to 

 detach them, frequently breaking tne shell before the 

 animal can be forced from its position. The name 

 chiton, is derived from the Greek, and means a coat 

 of mail. The animal in its structure is not less sin- 

 gular than the shell; its body is more or less 

 lengthened, depressed, or sub-cylindrical, obtuse 

 equally at both ends ; the abdomen provided with a 

 muscular disc or foot, adapted to climbing, but most 

 particularly to adhesion ; the back is sub-articulated, 

 and corresponds with the different valves ; the mouth 

 is anterior, and beneath, in the middle of a conside- 

 rable mass; it has neither eyes, tentacula, or jaws, but 

 it has a sort of straight tongue in the buccal cavity, 

 bristled with denticules. The organs of respiration 

 are branchial, and formed by a succession of small 

 branchiae beneath the turned edge of the mantle, 

 particularly at its back part. De Blainville places 

 the chiton in the second class Polyplajciphora, of his 

 sub-type of Malentozoaria, and he subdivides the 

 genus into the following well-defined species: 1st, 

 Such as are depressed with large valves, carinated, 

 much imbricated, the intermediate ones present- 

 ing well marked lateral areas, the limb of the 

 mantle regularly scaly, without hairy or silky tufts, 

 as in the C, squamosus here figured. 2ndly, The 

 sub-depressed species, with valves not carinated, 

 much imbricated, and without marked areas, the 

 lateral portions of the mantle covered with a species 



