12 UmTACRINUS: ITS STRUCTURE AND RELATIONS. 



have been some peculiar condition which brought them together in this 

 way, and it may have been the cause of their death. Dr. W. B. Carpenter^ 

 relates that on several occasions^ when he placed a lot of Antedons in 

 a basin of water and left them over night without any objects for attach- 

 ment, they were all found dead in the morning, " conglomerated at the 

 bottom of the basin, clinging to each other with their dorsal cirri, and 

 having their arms intertwined in such a manner as to suggest the idea that 

 they had died of asphyxia, produced by overcrowding ; " while if a like 

 lot of specimens were placed in a basin of the same size, with the same 

 quantity of water, and a number of rough stones for a basis of attachment, 

 all would be found in a healthy condition in the morning. The manner 

 of preservation of these fossils is precisely what would result from such 

 a conglomerated mass settling to the bottom and flattening out in the mud, 

 producing a lenticular plate, thickest in the middle, and thinning out to 

 a feather edge in all directions. What was the cause of their clinging 

 together in this way, and why it is that in the Niobrara Chalk we find them 

 only in this condition, are questions which I cannot undertake to answer. 

 They had no cirri, and must have ordinarily led a free life, — probably 

 pelagic, — for which, with their long and powerful arms as swimming 

 organs, they were well equipped. They probably swam in schools, as 

 Mr. Agassiz informs me the Comatulae sometimes do when moving from 

 point to point in Gorgonia groves. It is fair to presume that each of the 

 deposits as we find them is the remains of such a school, which from some 

 unknown cause became entangled in a confused mass, and perished in that 

 condition. It is possible that this may have happened during periods of 

 sexual activity. The living ComatulaB are unisexual, — the pinnules of 

 some individuals bearing ova, and others spermatozoa.! 



Another noteworthy fact is the entire absence in the Niobrara Chalk of 

 other crinoidal life. In the English Chalk, according to Mr. Bather,^ Uinta- 

 criniis occurs in the Marsiipites zone, and in direct association with Bourgiieti- 

 criniis. Schlueter § says that V. loestfalicus is associated with the following 

 forms : Bourgueticrinus elUpticiis, Pentacrinus cf. cingulatus, Marsupites ornatus, 

 and Antedon Lettensis. But here is not a sign of Bourgueticrinus (although it 

 has been found in Alabama), nor of any other Echinoderm. 



* Struct., etc., oi Antedon rosaceus, p. 701. 



t W. B. Carpenter : Struct., etc. of Antedon rosaceus, p. 690. 



X Geol. Mag. N. S., Decade IV., Vol. III., p. 444-5. 



§ Zeitsch. d. Deutsch. Geol. Gesell., 1878, p. 63. 



