110 
REPORT— 1847. 
scribed, or view them in an edgewise and endwise direction, they present u 
appearance remarkably ditierent from that which we have previously d^ 
scribed. In this case the whole of the ^tratllm appears to be composed ofa 
series of basaltiform columns, each column having the appearance of bang 
formed of a series of single cells regularly piled upon each other. Thisarisfs 
from the line of fracture ]>assing in a direction about equally oblique to the 
planes of the whole of the plates of prismatic cells. Trom this 'lescriptionof 
the alternating mode of Brmngemcrd of the plates of c»-lk, it will be oh 
vious, that if, on examining a shell we find a section parallel to the lines ol 
growth, with the plates c»f the central stratum agreeing in their direction ailh 
those lines, while those of the outer and inner ones arc at right angles to 
them, we shall find the apparent direction of tlie plates exactly the nwerseia 
each stratum if we view a second section of the .«tamo shell at right atiglolo 
the lines of growth. These modes of ari’angoment of the tissues are iDn- 
riable in the saino spocios- and genus, as Ikr aa 1 have had the opportunity of 
judging; and it is somewhat re?narkalde, that of the right genera exaounod, 
four assumed one mode of arrangement and four the othw. Thus, upon 
viewing sections parallel to the lines of growth of the shells, I tound that in 
CypTcBa, Cassis, Ainpullaria and hxUimus, the plates of tiie outer and ioMC 
stratum were parallel to the Uiiuw of growth, while tJiosc of the central one 
were at right angles to 'tlunu. On the contraiy, in Conus., Piiruk, Olw 
and Valuta, the j)Iates of the out(fr and inner stratum were at right angles to 
the lines of growth, and those ol' the central stratum parallel to them* And 
it is worthy of remark, that the porerllanous shells do not agree in the wiwe 
of arrangement of their tisnucs, as we find CifprtEa opposed to Cmits, Ohxa 
anil Voluta, and agreeing with Cassis, Ampullaria and BuUnm” 
91. The two foregoing accounts really agreiMiiuch more marly than niighj 
at first be suj)poscd. The existence of /Ansc lay tus in univalve slu-lls, sua 
the laminar coustitution of all these layers, is nunarked by both observen; 
and they further acconl with resimet to the opposition in die direction of the 
constituent laminai in the contiguous layers of shell. Tl»e ultimate cotopo 
sitioQ ot the individual laminm, however, is an important point of 
for whilst Mr. tlray describes them as marked with obscure oblique lioWi 
iu the direction of wldeh they separate when broken into long, narrow xlioai* 
bic crystals,” Mr. Bowerlmnk asserts that each lamina is composed of a dngk 
series of elongated, prismatic cells, adherent by their long sides. My o'™ 
observations le.ad ino to agree very deciiledly with the latter statemi'Ut. I 
think that after thu evidence of organic arrangement which has bern 
in the preceding descriptions of shelJ-strueturo, it can scarcely besuppo*^ 
that a disposition so extremely defitiite and constant as that which i« show" 
iu fig. 47 should have any other origin. The splintora into w hich tlie huuinf 
break up, when exouiined with a high maguifying power, are found to ha''^ 
much more the apivearance of the prisms of Pinna (see fig. 9 of Ibrmer 
port) than of simple crystals; and ai wo know that these prisms derive their 
shape from that ol the culls in wliieh they are moulded, it is pn»bable thst 
the former do so likewise. The best ovidcnci^ of their real character is de* 
rived from sections, iu wbit-h the Irregularity of their contour b sliowo- 
Although I quite accord with Mr. Bowerbaiik in the statcraeot, that from 
sections alone the structure of these shclU would probably be never 
torily made out, yet 1 coiuider that when wi; have learned to interpret tlie 
appearances they present by the knowledge first gained from the inspectioa 
of fractured surfaces, w'c may dcrivi* much valuable information through 
their means. In fig. 48 is shown a section of the shell of Ci/pr<so, take® 
perpendicularly to its suriaee, and in a direction transverse to the lines of 
