596 SAMPSON. [Vol. XI. 



of it, as an "apophysis," so that the shells deeply overlap at 

 the sides like scales. (Fig. i, ap). When the animal is ex- 

 tended, each shell covers the apophysis of the next posterior 

 shell and also a portion of the outer layer of the same shell 

 posterior to the apophysis. When the animal is contracted, 

 only the apophyses are covered, and the shells, therefore, do 

 not overlap in the middle line. The edges of the shells that 

 are bordered by the mantle (i.e., the anterior edge of the first, 

 the posterior edge of the last shell, and the lateral edges of 

 the intervening shells) are notched and firmly inserted in the 

 muscular tissue, and a small ridge of the mantle folds over 

 their extreme edges {cf. Figs. 4, 5, 7, 8, etc)}. This general 

 description applies to the various species which I have seen;^ 

 the principal variations in detail are in the degree of curvature 

 of the shells over the back and ends of the animal, and in the 

 thickness of the shell. 



The muscles have been worked out chiefly in transverse and 

 sagittal sections of C. olivaceus (found at Naples), though hori- 

 zontal sections and dissection of the same species have aided 

 in confirming the results ; dissections of C. viridis, Spengler, a 

 species from Jamaica that very closely resembles C. olivaceus, 

 were of still greater assistance, as the animals are larger. 

 An individual of this species is represented in Fig. 2 (the speci- 

 men was about 5 cm. in length after preservation in alcohol). 

 All the figures of sections are taken from preparations of 

 C. olivaceus. 



After writing the description of the muscles, an opportunity 

 occurred for making observations on living Chitons from Woods 

 HoU, probably C. apiculatus. 



The animal, never rapid in its movements, is capable of 

 assuming the greatest variety of positions, notwithstanding its 

 dorsal plate armor. It crawls slowly by means of the foot, and 

 can travel through the arc of a comparatively small circle. When 

 disturbed, it attaches itself firmly to the surface on which it 

 crawls. If the animal is removed, it rolls itself together until the 

 ventral surface of the anterior and posterior ends of the body 



1 C. pellis serpentis, C. olivaceus, C. granulatus, C. cajetanus, C. viridis, 

 Spengler. 



