PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 303 



CHITONES IRREGULARES. 



MOPALOIDEA. 



Genus MOPALIA Gray. 



Mopalia Gray, P. Z. S. 1847, pp. 65, 69, 169. — H. & A. Adams, Gen. Rec. Moll, i, p. 478, 



1854. (M. Eindsii Sby. ) 

 Molpalia Gray, Guide, p. 184, 1857 (err. typ.).— Gould, Otia, p. 118. 



Lorica regularis ; laminae longiores, snffultae ; v. ant. plirrifissata, v. 

 caet. unifissatse, ad caudam sinuatce ; sinus angnstus ; mucro medianus, 

 depressus ; suturae indentatse ; zona latior, setosa, interdum simplex, 

 interdum postiee fissata, interdum antice projectaj branchiae media3. 



Subg. Mopalia s. str. 



Zonae setae irregulariter obsitoe. (M. Hindsii Sby.) 

 Sect, a, normales ; Sect. /?, aberrantes. 



Subg. Placipharella Cpr. 



Zonae setae ad suturam fasciculatae. (P. vclata Cpr.) 

 Sect, a, zona antice dilatata. (P. velata Cpr.) 

 Sect, ft) zona et lorica normales. (P. sinuata Cpr.) 



The genus Mopalia is the most regular in growth of all the Irregular 

 Chitons. It is characterized by a hairy or lanugate girdle extending on 

 or between the valves to some extent in all the species, thin insertion- 

 plates with one slit on each side of the hind valve, which is waved in- 

 ward from behind in the median line. There is generally a pronounced 

 wave or slit in the tail end of the girdle, but this is an inconstant char- 

 acter even in the same species. The anterior valve has six or more 

 slits in most cases. The typical subgenus is divided into normal and 

 aberrant forms, the latter having the anterior portion of the girdle much 

 produced, as in M. Blainvillei Brod. ; both sections having the hairs irre- 

 gularly distributed. In Placipliorclla the hairs or part of them issue in 

 fasciculi from pores at the sutures. These also are divided into two sec- 

 tions, the first having the anteriorly expanded girdle as in the last sec- 

 tion of Mopalia, while the second resumes the normal type of shell and 

 girdle. Many species have been described, but it becomes necessary, 

 as will be seen, to reduce the number. 



Mopalia ciliata. 



Chiton ciliatuH Sowerby, Conch. 111. p. 79, 1838. — Reeve, Conch. Icon. Mon. Chi- 

 ton, pi. xix, f. 124, 1847. 



Mopalia ciliata H. & A. Adams, Gen. Rec. Moll, i, p. 478, 1854. 



Chiton 8etosu8 Sowerby, Beeehey's Voy. Zool. p. 150, pi. 41, f. 17, 1839 (not of Sow. 

 1832). 



Chiton Colliei Reeve, Conch. Icon. Mon. Chiton, pi. xxi, f. 136, 1848. 



Leptochiton Colliei H. &. A. Adams, Gey. Rec. Moll, i, p. 473, 1854. 



Chiton muscosus Gould, Proc. Boston Soc. Nat. Hist, ii, p. 145, July, 1^46 ; Moll. 



Expl. Exp. p. 313, f. 430, 1852. — H. & A. Adams, Gen. Rec. Moll, i, p. 475, 



1854.— Gould, Otia, p. G, 1862. 



