PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 303 



OHITONES IRREGULARES. 



MOPALOIDEA. 



Genus MOPALIA Gray. 



MopaUa Gray, P. Z. S. 1847, pp. 65, 69, 16l».— II. A: A. Adams, G.n. Ktu-. Moll, i, p. 478, 



1854. {M.Hindsii ^hj.) 

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



Lorica regiilaris ; lamina) longiores, suffultfe 5 v. ant. plurifissata, v. 

 CiBt. iinifissata?, ad eaudam sinuatse ; sinus angustus 5 niucro medianus, 

 depressus ; suturie indentata^ ; zona latior, setosa, interdum simplex, 

 interdum postice fissqta, interdum antice projecta ; branchiae mediae. 



Subg. Mopalia s. str. 



Zonae setse ii-regulariter obsita^. (If. Hindm Sby.) 

 Sect, a, normales ; Sect, ft, aben-antes. 



Subg. PlaciphorcUa Cpr. 



Zonae setae ad suturam fasciculata^. (i*. vclata Cpr.) 

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

 Sect. /?, zona et lorica normales. (P. sinttata Cpr.) 



The genus Mopalia is the most regular in groAvth 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 Cixch 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 

 sUts in most cases. The typical subgenus is di\dded 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 PlacipJiorella 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 gkdle as in the last sec- 

 tion of Mopalia^ while the second resumes the normal tyj)e of shell and 

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

 as will be seen, to reduce the number. 



Mopalia ciliata. 



Chiton dliatus Sowerby, Conch. 111. i>. 79, 1838. — Reovc, Couch. Icon. Mon. Chi- 

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



Mopalia ciliata II. & A. Adams, Gen. Kcc. Moll, i, p. 478, 1854. 



Chiton sclofiiis Sowerby, Beechey's Voy. Zool. p. 150, pi. 41, f. 17, 1839 (not of Sow. 

 1832). 



Chiton Collici Kocve, Conch. Icon. Mon. Chiton, -pi. xxi, f. 136, 1848. 



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



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

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

 1854.— Gould, Otia, p. 6, 1862. 



