20 



THE INOKGAXIC t'OXSTITUENTS OF MARINE IXVERTEBKATES. 



These figures fit in well with the others and even by themselves suggest a relation between 

 temperature and the magnesia content of crinoids. In the following table the entire series is 

 an-anged in the order of ascending magnesium carbonate, with the accessory data as to latitude 

 and locahty abbreviated. In this table the two analyses of Endoxocrinxis are averaged together, 

 and so also are tlie two of Isocrinufi. 



Percentage of magnesium curbonalc in crinnids. 



Genus. 



Locality. 



Heliometra 



Promachocrinus. . 



Ptilocrinus 



Anthometra 



Psathyrometra . . . 



Hathrometra 



Florometra 



Chlorometra 



Bythocrinus 



Pentametrocrinus. 

 Hypalocrinus . . - . 



Metacrinus 



Parametra 



Ptilometra 



Isocrimis 



Catoptometra 



Crinometra , 



Troinometia 



Endoxocrimis 



Pachylonietra 



Craspedometra 



Capillaster 



Zygometra 



Tropiometra 



Northern Japan . . . . 



Massachusetts 



Washinffton 



Eotti Island 



Gulf of Mexico 



Southern Japan . . . . 

 Philippine Islands. 

 Southern Japan . . . . 

 Philippine Islands. 



Australia , 



Cuba 



Philippine Islands. 



Cuba 



Brazil 



Cuba 



Philippine Islands. 

 Philippine Islands. 

 Philippine Islands. 



Am Islands 



Tobago 



Latitude. 



Northern Japan [ 43° N . 



Antarctic 67 



British Columbia ! 52"^ 



Antarctic I 67° 



44 

 39 

 47 

 10° 39' 



28° 38' 



S. 

 39' N. 

 S 

 N 



56' N. 



29' N. 



S.. 



N. 



34° N 



9°37'N.. 

 30° 58' N. 

 9°15'N.. 

 33°15'S.. 



24° N 



8°N 



23° 10' N. 

 25° 54' S.. 



24° N 



8° N 



5°12'N.. 



6°N 



5°-6° S... 

 11°25'N. 



The percentage of magnesium carbonate in Clihromefra is low for the latitude of tlie 

 locality, but that is doubtless due to the depth of the water (520 meters) in which the crinoid 

 lived. The probable temperature at that depth was between 7° and 10° C. 



From the foregoing table it is perfectly clear that the proportion of magnesium carbonate 

 in crinoids is in some way dependent on temperature. Temperature, however, is not entirely 

 dependent on latitude. Depth of water has also a distinct influence. The crinoids from rela- 

 tively shallow depths in tlie Tropics are highest in their magnesium content; those from the 

 Antarctic and the far north are lowest. The proportion given for No. 12, from the coast of 

 Massachusetts, is probably too low, for the specimen as analyzed contained over 6 per cent of 

 silica and sesquioxides — evident impurities, due to adherent mud from which the delicate 

 structure could not be wholly freed. If these are rejected, the magnesium carbonate is raised 

 from 9.36 to 10 per cent, which gives the crinoid a better and more probable rating. 



So far as we are aware such a peculiar relation between temperature and composition as 

 is here recorded has not been previously observed. To recognize it is one tiling; to account for 

 it is not so easy. At first we supposed that it might possibly be due to a difference in the form 

 of the more abundant carbonate — the less stable aragoiiite in tlie warm-water forms and calcite 

 in the crinoiils from colder regions. But tests by Meigen's reaction provetl that the organisms 

 were all calcitic, and so this supposition had to be abandoned. 



Mr. A. H. Clark, who is an authority on the crinoids, informs us that those from warm 

 regions have the most compact skeletons, the compactness bemg in general proportional to 

 the temperature and to some extent dependent upon the size of the individual. Heliometra, 

 for example, is the largest of the crinoids, its skeleton is one of the least compact, and its mag- 

 nesian content is hnvest among all tlic species examined. Structure as well as temperature 



