300 MOPALIA. 



Chiton lignosus GLD., Proc. Boston Soc. N. H. ii, p. 142, (July, 

 1846) ; Otia Conch, p. 3 ; U. S. Expl. Exped., p. 330, f. 424. 

 Chcetopleura lignosa GLD., Otia, p. 248. Mopalia lignosa CPR., 

 Rep. Br. Asso. 1863, p. 648. Chiton mercMi MIDD., Bull. Imp. 

 Acad. Sci. St. Petersb. vi, p. 20, 1846 ; Mai. Ross., i, p. 115, 1. 11, f. 

 5-6. Ch. eschscholtziiMiw., Bull. 1. c. p. 118, Mai. Ross., i, p. 114, 

 t. 11, f. 4 (young shell). Chiton montereyensis CPR., P. Z. S. 1855, 

 p. 231. Chiton vespertinus GLD., U. S. Expl. Exped. Moll. p. 323, 

 t. 426, 426a (1852). Chcetopleura vespertina GLD., Otia, p. 230, 

 242. Mopalia vespertina H. & A. AD., Gen. Rec. Moll, i, p. 479. 

 Mopalia simpsoni GRAY, P. Z. S. 1847, p. 69 ; H. & A. AD., Gen. 

 p. 479 ; and Brit. Mus. Coll. (name only ; never described. Type 

 examined by Cpr). Mopalia ciliata subsp. lignosa Gld., DALL, 

 Proc. U. S. Nat. Mus. 1878, p. 304. 



Typically the M. lignosa is extremely unlike M. muscosa, but I am 

 compelled to agree with Dall that there exist specimens completely 

 uniting the two. A number of published names are above added to 

 the long list of synonyms given by Dall (1. c.) ; and Ch. californieus 

 (Nutt.) Reeve, which Dall includes, is removed, as it belongs to the 

 genus Nuttallina. 



The typical lignosa (figs. 58, 59) is exactly equal to mercMi, to 

 montereyensis, and to the unpublished insignis Newc. (fig. 63). It 

 differs from the following form in the even puncturing of the sur- 

 face (obsolete on lateral areas), the peculiar painting, and white 

 interior. 



The principal mutations of this type of Mopalia are (1). Toward 

 still smoother forms entirely lacking pitted or reticulated sculpture, 

 having only a few subobsolete longitudinal wrinkles on the ridge, 

 the painting in concentric streaks (following growth marks) on each 

 valve. This is shown in figs. 60, 61, of pi. 63, the specimen illus- 

 trated being from Olympia, Washington. The C. vespertinus of 

 Gould is closely connected with this form, but is represented as 

 typically much pitted (fig. 62). It is stained with crimson within. 



(2). Form elevata (pi. 64, figs. 82, 83). More elevated, acutely 

 carinated, more or less pitted superficially, and either painted with 

 the pattern of typical lignos on a white, creamy or green ground, 

 or having concentric zig-zag blackish streaks (fig. 82), Divergence 

 about 90. The interior is bright green or blue. 



(3). Forms connecting with M. muscosa var. hindsii, having the 

 color pattern of lignosa, but the sculpture intermediate in char- 



