116 ISCHNOCHITON. 



Ch. punctulatissimus Sows., P. Z. S. 1832, p. 58 ; Conch. Illustr. 

 f. 9, 26; Moll. Beechey's Voyage p. 149, t. 40, f. 3, 3. REEVE, 

 Conch. Icon. t. 20, f. 129. 



The typical form of this species is described above, and figured 

 on my plate. It is characterized by the almost effaced but even 

 granulation, which is the same on both central and lateral areas, 

 although differing in direction; by the minutely freckled color pat- 

 tern, etc. 



Sowerby mentions a white variety with a black border and some- 

 what varied with black. This form I have not seen. It has been 

 illustrated by the figures in Captain Beechey's Voyage, H. M. S. 

 'Blossom,' and fig. 9 of the Conchological Illustrations. The latter 

 figure I have copied on my plate. 



I. IMITATOR Smith. PL 21, figs. 29-34. 



Shell elongate-ovate, moderately elevated, subangularly arched at 

 the middle, dirty white. Valves narrow, with a single notch on 

 each side, exhibiting small, slightly raised lateral areas, which 

 towards the margin have a few transverse strong grooves or marks 

 of growth. Front margin sloping very slightly on each side from 

 the middle in a posterior direction ; hind margin straight. Sculpt- 

 ure consisting of close flat granulation, exhibiting a somewhat 

 serial arrangement. Laminae of insertion [sutural plates] very thin, 

 with a wide sinus between them. Anterior valve sculptured like 

 the others, with fourteen fissures within, the thirteen teeth between 

 them being sharp and straight edged. Posterior valve with a cen- 

 tral mucro, from which there is a faint ridge on each side to the lat- 

 eral extremity, also marked with concentric lines of growth at 

 intervals and with the inner marginal fissures twelve in number. 

 Scales of the mantle minute, imbricating, ovate, arranged length- 

 wise ; under the microscope they appear very coarsely transversely 

 grooved. Length 11 mill.; diam. of fourth valve 5 mill. (Smith.) 



Tom Bay, Patagonia, oh the shore. 



CJi. (Ischnochitoii) imitator E. A. SMITH, P. Z. S. 1881, p. 35, t. 

 4, f. 13. 



6. Group of I. comptus. 



Surface evenly, minutely granulated, the lateral areas having 

 radiating riblets. Girdle scales nearly smooth. Japan, etc. 



