NO. 7 SEA-LILIES AND FEATHER-STARS — CLARK I7 



Bourgueticrinidse : Upper Jurassic to Recent. 



Rhizocrinus: Cretaceous (New Jersey) ; Eocene (Europe) ; Recent. 



Democrinus: In a recent breccia at Guadeloupe which also contained a 

 human skeleton ; Recent. 

 Apiocrinidas : Jurassic, Cretaceous and Recent. 

 Pentacrinidje : Trias to Recent. 



Isocrinus: Triassic and Jurassic; Recent. 

 Zygometridse : Jurassic to Recent. 



Catoptonietra: Jurassic to Recent. 



Eudiocrhms: Jurassic to Recent. 

 Holopodidse : Jurassic to Recent. 



Holopus: Tertiary to Recent. 



THE FOSSIL REPRESENTATIVES OF THE RECENT CRINOID 



GENERA 



Only a very few crinoid genera include both recent and fossil 

 species, and these are divided into two groups, (i) those occurring 

 only in the western Pacific {Eudiocriniis, Catoptomctra, Proisocrinus 

 and Carpenterocrinus, the species of the two last being apparently 

 congeneric with certain species of Millericrinus) and (2) those con- 

 fined to the western, or western and boreal, Atlantic {Isocrinus, 

 Rhisocrinus and Holopus). The recent distribution of these types 

 is thus seen to be the same as that of the living king or horseshoe 

 crabs (Xiphosuridse). 



Excepting only Proisocrinus riihcrrimus and Carpenterocrinus 

 mollis, all of the species of these genera are chiefly represented in 

 shallow water, and these two are the only ones which do not occur 

 within 100 fathoms of the surface; indeed the species of three of the 

 five other genera are entirely confined to water of less than 155 

 fathoms depth. 



The maximum representation is between the shore line and 200 

 fathoms, especially between 50 and 150 fathoms; as, taking the ocean 

 as a whole, we find at a depth of 200 fathoms a temperature of 

 50.1° F. and at 100 fathoms a temperature of 60.7° F. it is evident 

 that these genera are most abundantly represented within the opti- 

 mum temperature for crinoid life, which is between 50° and 65° F. 

 It is interesting to observe that (excepting for Proisocrinus and 

 Carpenterocrinus, each only known from a single dredge haul at tem- 

 peratures of 36° and 40° F.) the only increase in the numbers falls 

 between 50° and 64°, that is, within the optimum temperature for 

 crinoids, and is particularly emphasized between 56° and 64°, the 

 emphasis within the optimum temperature range being between 60° 

 and 65°. 



