abstracts: zoology 583 



employed in the study of domestic horses; and to throw some hght 

 on the elements which have contributed to the formation of that 

 assemblage of horses which bears the name Equus caballus. 



O. P. H. 



ZOOLOGY. — The relation between the maximum and the average bathy- 

 metric range, and the mean and the average depth of habitat, in the 

 subfamilies and higher groups of recent crinoids. Austin H. Clark. 

 American Journal of Science, 40: 67-74. July, 1915. 

 In general the more specialized famiHes possess small, and the more 

 generalized large, bathymetric ranges; the thermal adaptability of the 

 groups increases with specialization. The average range of the fami- 

 lies of recent crinoids is very nearly the same as, but shghtly more 

 than, the average depth of habitat. A. H. C. 



ZOOLOGY. — A study of the recent crinoids which are coiigeneric with 

 fossil species. Austin H. Clark. American Journal of Science, 

 40:60-66. July, 1915. 



The eight genera of recent crinoids which include fossil species fall 

 into the following three groups: (1) Genera confined to the western 

 Pacific; Eudiocrinus, Catoptornetra, Proisocrinus and Carpenterocrinus; 

 (2) genera confined to the western, or western and northern, Atlantic, 

 but occurring as fossils in the Indo-Pacific basin ; Isocrinus, Rhizocrinus 

 and Holopus; (3) genus common to the Indo-Pacific and Atlantic; 

 Democrinus. 



All but one of these genera are chiefly developed in shallow water; 

 this single exception is also the only one which, so far as we know, 

 does not occur within 100 fathoms of the surface, three of the others 

 being entirely confined to water of less than 155 fathoms in depth. 



In the total range, average range, and mean depth of habitat these 

 genera show a close approximation to the genera peculiar to the At- 

 lantic, in contrast to those peculiar to the Indo-Pacific, which have a 

 much greater total range but lesser average range and mean depth of 

 habitat, and to those common to both oceans, which have a much greater 

 average range and mean depth of habitat, as well as total range. In 

 depth the maximum representation is between 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, and at 

 100 fathoms 60? 7, it is evident that these genera are most strongly 

 represented within the optimum temperature for crinoid life, which is 

 between 50° and 65°. A. H. C. 



