498 HYATT'S REVISION OF THE 



favorable. These last, then, are probably the direct causes of the inferiority of the skel- 

 etons of the commercial varieties found in this association.^ 



These views, as a whole, therefore depend for confirmation upon the accuracy of the cal- 

 culations with regard to temperature, and upon the following facts : that the inferiority of 

 the skeleton, which is common at Key West, with the same isochrymal as the Red Sea, is not 

 found to the same degree in the sponges growing in the clearer waters of the latter ; that 

 the coarsest quality of all the Mediterranean sponges, the "Gerbis sort," and other coarse 

 " sorts," grow in localities along the coast, where they are most subject to the action of 

 susjjended matter in the water ; but all of these are, however, on account of the clearness 

 and medium temperature of the Mediterranean waters, as comjiared with those of other seas, 

 of much finer quality ; that the coarser kinds of the same quality or variety grow nearest 

 the shore, and the finer kinds in deeper water, and also accoi'ding to Nassau spongers, are 

 more apt to occur upon marly groimd, where the sediment is finer than upon other kinds 

 of bottom ; and lastly, that the inverse ratio between the quantity and even the prevalence 

 of different kinds of sediment, such as sand grains or spicules, and the resiliency and flex- 

 ibility of the fibres may be demonstrated with the microscope in any series of specimens. 



It may be well to notice, however, that the openness, or apertion, which usually accom- 

 panies and appears to correllate with coarseness of the fibre, cannot be accounted for in this 

 complicated way, but, strictly speaking, must be considered as one of the elements of infe- 

 riority which invariably accompanies a skeleton having a loose microscopical texture or 

 mesh, and harsh, inelastic, or easily torn fibres, but is also, though rarely, found in skele- 

 tons of very fine quality, especially at an early age. Thus it may be said, that it is un- 

 doubtedly a common cliaracteristic of all the inferior qualities of Mediterranean, and of all 

 the Carribean commercial sponges, without exception, which, though they may have very 

 fine or very coarse or inelastic fibres, are always permeated in the interior, and have the 

 surface also cut up, by larger and more numerous canals than the corresponding Mediterra- 

 nean species. The Austrahan species of the genus Spongia, though coarser in fibre than 

 the Carribean forms, are equally open, and are harder when dry than any of the former, 

 except certain rare varieties of Spongia agaricina and Spongia discus. In this connection 

 it may be appropriate to call attention to the forms, all belonging to the unmarketable 

 varieties of the genus Spongia which have been found in hot climates, as for example, 

 at the Mauritius and the Hawaiian Islands with an isotherm for the coldest months of 74°, 

 Kingsmill Islands and Feegee Islands with one of 80°, at various places in the Bay of 

 Panama and Gulf of Mexico with isotherms for January of from 74° to 80°. The ex- 

 tremes of temperature are represented at Stono Inlet, South Carolina, with a marine 

 isochryme of about 51°, and Sydney, AustraUa, with one of 5G°. The evidence aflbrded by 

 these, all of which have very open, coarse, and brittle skeletons, therefore confirms the 

 opinion, that this characteiistic of apertion may be with great probabihty attributed per- 

 haps exclusively to the influence of an unfavorable temperature, which, if the limits sug- 

 gested in this paper are correct, might be either the amount of cold indicated by an 



J What effect the superior density of Mediterranean water vestigated, and this may prove to be of greater importance, 



may have, it would not be possible at present to say, the data since the variation is probably much greater in this respect, 



being insufficient, but it is probably very slight. The chemi- especially in the vicinity of coral reefs, 

 cal composition of the water has also not been sufficiently in- 



