CH/ETOPLEURA. 27 



This very peculiar shell resembles Mopalia blainvillei in mantle 

 and mucro ; and Nuttallina in the long, smooth plates, separated by 

 a deep, not laminated sinus. The side slits, however, are single and 

 deep instead of duplicate and angular, as in that genus; the poste- 

 rior plates are not thrown forward nor waved as in Mopalia. Leav- 

 ing out of view the anterior prolongation of the mantle, which is a 

 variable character even among Mopalia, it may be regarded as a 

 partially covered Tonicella. The slits are abnormally few, as in 

 Leptoplax. But for the characters of the tail plate I should have 

 considered it intermediate between Mopalia and Katherina. (Cpr.) 



Genus VII. CHCETOPLEURA Shuttleworth, 1853. 



Chcetopleura SHUTTLW., Diagn. neuer Moll. no. 4, iiber den Bau 

 der Chitoniden, etc., in Bern. Mittheil. p. 66, June, 1853 (=Acan- 

 thopleura Gray, ex parte). Chcetopleiira CPR. MS. and DALL, Proc. 

 U. S. Nat. Mus. 1878, p. 329, type C. peruviana Lam. Acantho- 

 pleura, GRAY, Guide Moll. B. M. p. 183. 



Valves as in Ischnochiton ; eaves solid ; girdle leathery, more or 

 less hairy ; gills extending almost or entirely to the front end of the 

 foot. 



The present group seems to me to stand naturally on the confines 

 of the Ischnochitonoid series, having decided relations to the true 

 Chitons and especially to Tonicia. 



Carpenter made a subgenus, Maugerella, under Chcetopleura, for 

 a Radsioid Californian form, which I have excluded from the genus, 

 as its affinities are with the Radsioid Ischnochitons. The following 

 able discussion of this genus is from Carpenter's MS. : 



Shuttleworth, in distinguishing this genus from Acanthopleura by 

 the mantle characters only, does not seem to have observed the co- 

 ordinate differences in the hind valve and the insertion plates. 

 Messrs Adams united to this genus Eudoxochiton and Craspedo- 

 chiton which do not belong to the same section. Gray, in his 

 " Guide," p. 183, ignores the genera of Shuttleworth, but preserves 

 the distinction between Chsetopleura and Acanthopleura. Most 

 unfortunately, however, he chooses to keep the name Acanthopleura 

 for Chsetopleura of Shuttleworth and Add., and makes a fresh name 

 Maugeria for the restricted Acanthopleura of Shuttleworth and 

 Add. Even if Shuttleworth had been unwise in his mode of 

 division, he would have been entitled to precedence ; but fortunately 

 he kept Acanthopleura for the first section of Guilding's group, 



