a 



two Specimens of Rhynchopora Geinitziana. 125 



Neither specimen exhibits any portions of an impression of the 

 inner surface of the valves. 



1. The specimen with the umbone of the large valve broken off. — 

 The outer or original surface of this specimen seems to have 

 disappeared, while in some places it is obscured with foreign 

 matter. In the former condition, the remaining test displays 

 numerous black dots*. In a few places the specimen has been 

 a little filed or cut down. The test that remains is, in several 

 places, of considerable thickness, which is well exhibited on the 

 fractured portion, where the umbone is broken off. At this part 

 the black dots are seen (as represented in the surface-figure and 

 longitudinal section, figs. 1 and 2) not only on the surfaces a 

 and e, but also on the intermediate por- p. , 



tion b, A broken part on the small ^* 



valve, between the umbone and the an- 

 terior margin, also shows the test to be 

 of considerable thickness ; and in certain _^- 

 lights some of the black dots appeared as 

 if they formed the terminations of fine 

 hair-like lines passing down through its pj- 2. 



thickness. In no instance could I con- o, 



vince myself that they were " mere acci- <^ \ \ 



dental results of infiltration," as main- V ■ • ■ -'i 



tained by Dr. Carpenter in one of his '^^^^ ' 



letters to me : their regularity completely forbids the idea. 

 Black dots are nearly everywhere exhibited on the abraded 

 surface of this valve : the exceptional cases will be noticed here- 

 after. 



The observations stated completely prove, in my opinion, that 

 the black dots are not simply " pits upon the internal surface of 

 the shell;" or they ought not to be seen on the surface of every 

 layer of tissue exposed : the whole of the layers, be it understood, 

 form a series of considerable thickness. On the contrary, seen 

 under the circumstances named, they cannot but represent 

 broken transverse sections of tubular perforations, similar to 

 those characteristic of the Terebratulida, and passing through 

 the entire thickness of their shell-substance. I am disposed to 

 regard their dark colour as due to the carbonaceous residuum 

 of the membrane with which the perforations were originally 

 occupied. The perforations of fossil Terebratulida are often 

 filled with a similarly coloured matter : this is remarkably the 

 case with some specimens before me of Waldheimia ornitho- 

 cephala, which in this respect offer so striking an analogy to 

 what is seen in the Permian species under consideration as to 



* My observations, made with a Stanhope lens, were most successful 

 when made in subdued sunlight. 



