AND VARIETIKS OF CHlTOMD« AND ACM.EID.*:. 276 



d'txtnritlhiix, rrehrc fJfirvsxntin, jugo acuto ; tir. lot. conff^ V\., 

 V(i/if/ixi(i>i)is, oinjustin, tufierciilia aiif/uxtia : intiis tnarjjiiiifjva 

 suturalifjiig jt'is/irls pfatinti.t, hand tnfjcrcufo/iis, hand i<iniiofi.s; 

 lam. insert, vt iinien, nitiit nngusto, atl juyum aiiyiilato. Valra 

 antica cosfis x., riiH<lis, U'lf/iinHs : intus ut otitea, sfd fissvrig 

 viii. J (ilea jioslica Mitcruuc puslico, jilininfo; jiarff jumticu 

 e.rj)aiisa, huud roncaca, rostis circ. vii. valiJissimis : intus 

 hiiiiina circ. \\\.-p\'<,s<t, subjirmnln ptunatn. 

 With a strung •ii-iu ral reseiiil)lancc to I, efcnensis, the differences 

 in detail in the only two specimens examined, as above stated, ap- 

 pear ot" specific iinporlance. If only varietal, it is ecpially im[»ortant 

 to notice how nincli ciiaiiije is tolerated by the liabits of the animal. 

 It may be the shell called Chiton cluthratus by Prof. Adams, of wliich 

 there were no duplicates to compare. It otters a still more marked 

 transition to Callochiton, the margin of the posterior valve being 

 somewhat pectinated by the great projection of the ribs. 



"Callochiton" pilchellus: diagn. auct. 



Extus areis centr. linris interdnm parullelis, infordinn rttdinn' 



tihus, ruynse ^crohiridatis ; ar. hit. cosiis ii., vuliiliiisimis, im- 



bricato-u(n/o«is : ra/ca antica costis siniiliius circ. ix. ; r. 



post, area ccntrali lata ; mucrone suhposfico, phtnato ; parte 



postica costis \u. siniililjus, niediunis curtissiitiis, eucuriatis : 



palfio sqiianndis mimitis imbricatis. Intus v. ant. subyrunda 



(lit in Ischiiochitonej nnniila, scd a costis pvctinritu ; dentibus 



acutis, intus linen undulata secundum castas instructa, extus 



concavis, parte convexa costnrum incisis : v. medianis similiter 



pectinatis, lannnis secundum castas diar/. uniscissis : laminis 



sufurahbus medio continuis, lute sinnatis; suturis posticis a 



sculptura externa yranulatis : v. post. \\\.-Iobata, maryinibus 



pfanatis, laminis dense compressis incrassatis ; dentibus obtu- 



sissimis, appressis, ham/ cctantibus, subobsoletis, extrorsum 



planutis, ut in i\ ant. Jissis ; interdum Jissuris quoque in par- 



tibus concaris. 



As I have seen no published diagnosis of the very peculiar type of 



insertion-plates ol)served in this species, which has hitherto been too 



rare to allow working naturalists an opportunity of dissection, I have 



given a minute description. The plates of insertion, as well as the 



exterior eaves, are scalloped by the strong ribs, and alternate with 



them. In the posterior valve the eaves are flattened outwards, in 



closely appressed layers, the blunt, ill-developed insertion-teeth 



lying flat upon them. The valves easily separate from the mantle, 



when immersed in water. Outside, the species is easily recognized 



by the two strong ribs of the diagonal areas, the central pitted in 



somewhat branching rows, and the ribs on the curiously flattened 



posterior valve resembling a clenched fist. 



ACM.BA (? FLOCCATA, var.) FILOSA. 



A. t. "A. mesoleucae "/wwia et indole simili ; sed sculptura midto 



267 



