﻿schuchert] siluric and devonic cystidea 267 



Moreover, if Camarocrinus is a float, why is it that the great 

 majority of the bulbs are found in the strata with the stalk end down- 

 ward? Assuming for the present that these bodies are the air-filled 

 floats of some crinoid, it must be granted, on the basis of the wide 

 disseiuinati.nl of other shelled organisms with hollow cavities (as the 

 shells of Spirilla, Nautilus, and Ammonites) that the bulbs of 

 Camarocrinus would continue to float for some time (possibly for 

 hundreds of miles) after the crown and stalk bad decayed. The 

 latter portions would be dropped over one part of the sea bottom, 

 while the bulb would sink later in another region. On account of 

 its double and interlocked walls and interior braces, the dead bulb 

 would continue to drift with the currents, as in the living condition, 

 i. e., with the stalk downward, because the weightiest part is at this 



The weight of this specimen was multiplied by the number of equal fragments 

 estimated to make a bulb ,V j inches in diameter. It therefore seems to the 

 writer that the weight is considerably overestimated. 



The weight of the calcareous skeleton in a dry specimen of Echinus escu- 

 lentus L., nearly 4 inches in diameter and without spines and jaws, is 2 ounces. 

 Another dry echinus, E. gracilis, with spines, jaws, and the dried remainder 

 of the soft parts, nearly 3 1 _> inches in diameter, weighs but 1 , V, ounces. These 

 figures indicate that a dry Camarocrinus before mineralization probably did 

 nol weigh 4 ounces. 



(2) A specimen of Camarocrinus 3 l /> inches in diameter, he estimates, would 

 contain about 8 cubic inches of air, and therefore lacked the capacity neces- 

 sary to Moat as large and heavy a crinoid as Scyphocrinus. This estimate is 

 in error, as the contents of such a bulb is about 22 cubic inches. 



(3) A specimen of the crown and stem of a living Isocrinus decorus (Ha- 

 vana) 16 inches long, also in the dry state, weighs but three-sixteenths of an 

 ounce. If Scyphocrinus is 4 times as large and 8 times as heavy as the Iso- 

 crinus, then the dry skeleton of the former would weigh only i T /> ounces. 



The writer realizes that these estimates may not be the real weight in the 

 living organisms, and also that the weight of the soft parts is not considered 

 (these, however, need hardly be considered, as the specific gravity of the soft 

 parts is but one-tenth heavier than water). The only point he wishes to em- 

 phasize is the relative weights of the parts in relation to the floating capacity 

 of the bulb. A sphere 3^2 inches in diameter has a cubical content of a little 

 more than 22 inches. A cubic inch of water weighs 252.45 gr. A 3 I /4-inch 

 sphere will therefore displace or float above the water (distilled) a weight 

 equal to nearly 13 ounces. In sea water it will be nearly twice as much, and 

 if suspension in sea water alone is considered, it will be nearly two and a 

 half times that of floating it in distilled water. A dry skeleton of a Scypho- 

 crinus with a crown about 1 foot in length and a stalk 3 feet long, with a 

 3^-inch bulb, is estimated to weigh not over 6 ounces. When one considers 

 that these bulbs attain a diameter of 5 inches, and even larger in Bohemia, 

 while the Scyphocrinus crown used in the above estimates is one of the larg- 

 est, it is seen that these bulbs are abundantly able to suspend a stalk and 

 crown of so ponderous a species as Scyphocrinus elcgans. 



