114 
REPORT—1847. 
remainder of the figure shows the appearance of the internal layer under po- 
larized light (§ 92) ; its lamina, which have their planes directed toffaji 
the apex and base of the Cone, being cut edgewise, or nearly so. If a so* 
tion be taken across the upper part of the cone so as to traverse the middle 
or cellular layer in the direction of its thickness, its prismatic ebameter (o- 
tirely conformable to tbut of Pinna) will be made evident. The dircctiwb 
of the planes of the lamina.’ of the internal and extermil layers of Pattikm 
at right angles to each other, instead of being conformable to each otliersod 
at right angles to thi* middle one, as they are when the latter haa a rouifar 
structure. 1 have noticed, on fractured surfaces of this shell, an arraujs 
meut which has been noticed and describeil br Mr. Boworbank iuTcjrtfdtp 
other Univalve shells. *♦ When the prismatic .shells are fmetured aentsstiw 
axes, they do not prc-sent such surfaces as might naturally be expected fron 
crystallized bodies, but have an uneven, rotigh, and somowhat spicalaifil 
appearance. Upon exiuniniiig these iwgnns from the innersurface of a hA 
Vbluta nodoxa) from the London clay, I found that, when broken atri§lii 
angles to their axes, they resolved themselves into escccdinglrminutefilifW' 
so that each broken end resembled .a worn-out camdVhair pncil. ifdie» 
penciUlikt! cuds be crushed in a little water, on a slip of glass, and rieffed bj 
transmitted light with a power of 1000 linear, wo find innumerable transpa’ 
rent filaments, which appear to have a cylindrical form; hut this point ctH’ 
not be determined with certainty from their extreme miimtene&s. They vary 
m size ; but one of about the average dinionslons, which I measured, was fit 
1-80,000th of an inch in diameter, and many of them were not above hilfm 
arge. Among these spicular bodies there were inanysinall fnigiucutsofp!at<*i 
ormed of similar minute fibres, disposed acro.s 9 each other at right BtiglW 
so as very much to resemble a piece of line linen.” No trace of these can be 
tietected in tho thinnest and most carefully made sections of the shell; 
cannot agree with Mr. Bowerbank in the belief that t}»*y are the result 
arrangement. They seem to me rather due to the pcculiarcf?- 
. p txggregaiion of the calcareous particles, which causes them to asjuwf 
disturbed by tho shock of the fracture. Such JJ 
Brewstn^r*^® uncommon, I believe, in mineral bodies. Thus Sir D- 
nuS4 • 1*"* Journ. of Science, No. I.p. 108) that a crystal 
hitcfrilni" ri,’**!’? the faces of the fractnrfl appeared sli**- 
of s l>Iack velvet, owing to their being covered with afioe^ 
^ S "of X'gllgh^^ 
thrdetaii,^'!^? arrangement prevails as in 
P ^nated "r " u^tomal layer, which is usually i"; 
se^n in “’«ttor, docs not exhibit the laminations which ^ 
Tue urf everywhere a delicate 
part of riiul to the surface. The sup^ 
bito ite s il'l ‘s.pcrlorated by large canals which pass down obhqf^f 
Tim '-thont pmmtru,i„g%o far as tho middle layer (dg,;^ 
braluta is hv canals, which rtmiind us of the perforations of 
(fig 52 a) ’whi't ** great toughness, there is a layer of mi'’"*® \ . 
lay^r fibres ; and Mow this 
The internal pavement-like cells, as m 
external t'»l>avethc same nearIy-homogeaeouaiextare«‘J’» 
normal general arrangement is 
, but in the shelly base of the latter is a very curious 
