306 Dr. W. B. Carpenter on the Microscopic Structure 



Russian specimens of the fossil shell in question, and therefore 

 passing, more or less exactly, in a direction parallel to that sur- 

 face ; and (2) of a transparent vertical section of a German speci- 

 men. As these specimens were supplied to me by Mr. Davidson, 

 there can be no doubt of their authenticity. 



Some of the transparent lamellae exhibit distinct and regular 

 perforations, filled with black matter, of considerable size ; and 

 had these lamellse been my sole materials of judgment, I should 

 have readily accorded with the description of Prof. King. But, 

 as I stated when the matter was formerly under discussion (Ann. 

 Nat. Hist. March 1857, p. 214), this appearance is presented 

 only by lamellse taken from abraded surfaces, and therefore be- 

 longing to the internal layer of the shell. In a transparent 

 fragment in which the natural surface of the shell is partially 

 preserved, the large and regular black spots are seen only near 

 one edge ; towards the middle they give place to small black 

 dots, so irregular in size and form as scarcely to be distinguish- 

 able from others which are obviously due to infiltrating deposit; 

 and towards the other side they are wanting altogether. Now 

 in the whole of this specimen the characteristic structure of 

 the shell is most perfectly preserved, so that the absence of 

 the marks of perforation cannot be ascribed to metamorphic 

 action. 



The key to this variety in the appearances presented by pa- 

 rallel lamellse is afi'orded by the vertical section. In one part 

 (fl) of this section there 



is an obvious deficiency -«.^^>- ^^ c 



of the external layer of '^iHttL..^^^^^ ^ "^^^'^'^ 



the shell, and the per- ^' 



forations are seen to pass ^ 



continuously through Vertical section of a portion of the sheU of 

 the remaining internal Bki/nchojpora Geinitziana. 



layer. But in another part [b c), the external layer is preserved 

 in great part, if not the whole, of its thickness ; and this layer is 

 plainly seen not to be perforated at all, the passages all stopping 

 short of it, sometimes ending abruptly in rounded terminations 

 {b), sometimes more pointedly {cd). Hence it is obvious that 

 if the plane of a parallel section pass along the Hue d e, it will 

 show at a large perforations, at c small perforations, and at b c' 

 none at all, which is exactly what is seen in the specimen pre- 

 viously described. And further, as the transparence of the shell 

 allows the large black spots with which the inner layer is regu- 

 larly marked to be plainly seen through the outer layer, even 

 when this is perfectly preserved, it is easy to understand how 

 readily the conclusion might be drawn from incomplete obser- 

 vation, that the perforations extend through the whole thickness 



