AND VARIETIES OF CHITONID^ AND ACM.EIDjE. 276 



distantibus, crebre decussatis, jugo acuto ; ar. lat. costis ii., 

 validissimis, ancjustis, tuberculis angustis : intus marginibus 

 suturalibus posticis planatis, haud tuberculosis, haud sinuatis; 

 lam. insert, ut antea, sinu angusto, adjiigum angulato. Valva 

 antica costis x., validis, avgustis: intus ut antea, sed fissuris 

 viii. Valva postica mucrone postico, planato; parte postica 

 expansa, haud concava, costis circ. vii. validissimis : intus 

 lamina circ. y'n.-Jissa, subgrunda planata. 

 With a strong general resemblance to I, elenensis, the differences 

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

 pear of specific importance. If only varietal, it is equally important 

 to notice how much change is tolerated by the habits of the animal. 

 It may be the shell called Chiton clathratushj Prof. Adams, of which 

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

 transition to Callochiton, the margin of the posterior valve being 

 somewhat pectinated by the great projection of the ribs. 



" Callochiton " ptjlchellus : diagn. auct. 



Extus areis centr. lineis interdum parallelis, interdum radian- 



tibus, rugose scrobiculatis ; ar. lat. costis ii., validissimis, im- 



hricato-nndons : valva antica costis similibus circ. ix. : v. 



post, area centrali lata; mucrone subpostico, planato; parte 



postica costis vii. similibus, medianis curtissimis, excurvatis : 



pallio squamulis minutis imbricatis. Intus v. ant. subgrunda 



(ut in Ischnochitone^ munita, sed a costis pectinata ; dentibus 



acutis, intus linea uadulata secundum costas instructa, extus 



concavis, parte convexa costarum incisis : v. medianis similiter 



pectinatis, laminis secundum costas diag. uniscissis : laminis 



suturalibus medio continuis, late sinuatis; suturis posticis a 



sculptura externa granulatis : v. post. Vi\.-lobata, marginibus 



planatis, laminis dense compressis incrassatis ; dentibus obtu- 



sissimis, appressis, haud extanfibus, subobsoletis, extrorsam 



planatis, ut in v. ant. Jissis; interdum fissuris quoque in par- 



tibus concavis. 



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



insertion-plates observed 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 postei'ior 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 iu 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. 



ACMiBA (? FLOCCATA, Var.) FILOSA. 



A. t. "A. mesolencas" forma et indole simili ; sed sculptura midto 



267 



