1865.] 



CARPENTER — STRUCTURE OF EOZOoN. 



113 



Although the general plan of growth described by Dr. Dawson, 

 and exhibited in his photographs of vertical sections of the fossil, 

 is undoubtedly that which is typical of Eozoon, yet I find that the 

 acervuline mode of growth, also mentioned by Dr. Dawson, very 

 frequently takes its place in the more superficial parts, where the 

 chambers, which are arranged in regular tiers in the laminated 

 portions, are heaped one upon another without any regularity, as is 

 particularly well shown in some decalcified specimens which I have 

 myself prepared from the slices last put into my hands. I see no 

 indication that this departure from the normal type of structure 

 has resulted from an injury ; the transition from the regular to the 

 irregular mode of increase not being abrupt, but gradual. Nor 

 should I be disposed to regard it as a monstrosity ; since there are 



^amms^ 



4. Diagram illustrating the structure of Eozoox. 

 A', A', A'. Three chambers of one layer, communicating with each other 

 directly at a, and by three passages through a shelly par- 

 tition at b. 

 A 2 , A 2 , A 2 . Three chambers of a more -superficial layer. 



B, B, B. Proper wall of the chambers, composed of finely tubular shell- 



substance. 



C, C, C. Intermediate or supplemental skeleton, traversed by D, a 



stolon of communication between two chambers of different 

 layers, and by E, E, a canal-system originating in the lacu- 

 nar space P. 



many other Foramhufera in which an originally definite plan of 

 growth gives place, in a later stage, to a like acervuline piling-up of 

 chambers. 



In regard to the form and relations of the chambers, I have little 

 Vol. II. h No. 2. 



