1865.] BILLINGS — SILURIAN AND DEVONIAN FOSSILS. 407 



dary's wheel, and polished, the form of the greater part of the cup 

 is well displayed in section. The fossil itself consists of yellowish 

 white calcareous rock, but the cup is filled with grey compact 

 limestone, holding minute fragments of shells, trilobites, and 

 crinoids. The depth of the cavity is thirty lines, and its width 

 at the bottom eight lines. At eighteen lines from the bottom 

 its width is eleven lines, and it then suddenly widens to 

 thirteen lines. Above this the walls are obscurely preserved, 

 although it can be made out that, on one side, they ex- 

 tend at least one inch higher. The central tube is, in this speci- 

 men, filled with calcareous spar, and very indistinctly defined. 

 Remains of several of the septa can, however, be seen — their con- 

 cave side upwards towards the bottom of the cup. 



The second specimen is also a fragment, consisting of the upper 

 fourteen inches. The diameter at the lower end, where broken 

 off, is eighteen lines, and at the supposed margin of the cup 

 thirteen lines. Diameter of the central tube about four lines. 

 Depth of the cup, seven and one-fourth inches. The cup is 

 of the same width as the central tube throughout, except 

 in the upper two inches, where it expands to the width of 

 eight lines. The margin of the cup is not well preserved, but as in 

 the last specimen noticed, is broken so that the entire outline can- 

 not be made out clearly. In this specimen it may be that the 

 cup was not more than two or three inches in depth when perfect, 

 and that its apparent extension downwards is due to the destruc- 

 tion of the septa in the central tube below the bottom. 



The third example is a large specimen of B. undulata, ten feet 

 five inches in length, eight inches in diameter at the base, and six 

 and a-half at the upper extremity. The cup, exposed by a frac- 

 ture, is nine inches in depth ; width at the bottom about nine 

 lines ; at four inches above — twenty one lines ; then suddenly 

 enlarging to three inches. 



In none of these specimens is the margin of the supposed cup 

 perfect. Not the slightest indication of radiating septa can be de- 

 tected. In order to determine all the characters of this portion of the 

 fossil, specimens with the cup entirely empty and with the margin 

 perfect as it was during the life of the animal, are required. Numerous 

 individuals were seen lying imbedded in the rocks with the larger 

 end well preserved, but in most instances on approaching the smaller 

 extremity, it was found to become more and more obscure until it 

 at length blended with the matrix. It would thus appear that the 



