PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 303 



CHITONES IRREGULARES. 



MOPALOIDEA. 



Genus MOPALIA Gray. 



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



1854. ( M. Hindsii Sby. ) 

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



Lorica regnlaris ; laminse longiores, snffulttE ; v. aut. plurifissat4, v. 

 esRt. unifissat.T, ad caudam sinuatse ; sinus angustus ; mucro medianns, 

 depressus; suturos indentatae ; zona latior, setosii, interdum. simplex, 

 interdum postice fissata, interdum antice projecta; branchise mediae. 



Subg. MopaJia s. str. 



Zonte setai irregulariter obsitaj. {M. Hindsii Sby.) 

 Sect, a, uoiinales ; Sect. (3, aberrantes. 



Subg. PlaeipliorcUa Cpr. 



Zonae seta? ad suturam fasciculatae. (P. velata Cpr.) 

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

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



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

 Chitons. It is characterized by a hairy or lauugate 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 luxe. 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 tj"pical subgenus is di\ided into normal and 

 aberrant forms, the latter having the anterior i)ortion of the girdle much 

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

 gularly distributed. In Flaaqjhorella the hau-s or part of them issue in 

 fasciculi from i)ores 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 ciliatu.'i 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 setosus Sowerby, Beechcy's Voy. Zool. j). 150, pi. 41, f. 17, 1839 (not of Sow. 

 1832). 



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



Leptochiton CoUiei H. & A. Adams, Gen. Rec. Moll, i, p. 473, 1854. 



Chiton muscosm Gould, Proc. Boston Soc. Nat. Hist, ii, p. 145, July, 1846; MolL 

 Expl. Exp. p. 313, f. 436, 1852.— H. & A. Adams, Gen. Rec. Moll, i, p. 475, 

 1854.— Gould, Otia, p. 6, 1862. 



