. NORTH AMERICAN PORIFERiE. PART II. 491 



of the Mediterranean, which in the Western Basin vai'ies from 1.0280 to 1.0284 in the neigh- 

 borhood of Sicily, and is even denser in the Eastern Basin, rising between Malta and Crete 

 from 1.0284 to 1.0288. If this want of an average amount of salinity did not account for 

 the absence of the genus Spongia, and possibly all the Keratosa from the Black Sea, the 

 temperature of the water would, the winters being exceedingly severe. The isotherms 

 of the summer months, according to Carpenter,^ range between 70°-80°, while in the 

 winter the variation is 30°-40°. This extreme cold is due to the sharp northeast winds 

 which come over the snow-clad plains of Russia from the Arctic regions. Ice is therefore 

 very abundant along the northern shores in winter, and the temperature of the water 

 probably falls quite low, since in the temperature taken Ijy Commander Wharton,^ of which 

 unfortunately only one observation is recorded as made in October, the water was only 62° 

 to a depth of 30 fathoms, then a cold current of 54^, and below tliis again the thermometer 

 rose to 60°. 



If either the temperature or density of the water had been exceptional, we might have 

 gained some additional information, but as it is, we cannot assume that either cause would 

 have beeri sufficient to account for the absence of the Spongite from the Euxine. According 

 to Carpenter, in his articles on the Mediterranean and Black Sea, there is a strong current 

 continually flowing at the depth of twenty fathoms from the Mediterranean into the Black 

 Sea, and a return surface current from the Black Sea into the Mediterranean. The 

 sponges occur necessarily in the shallower waters of the Sea of Marmora, since they 

 are said by .Von Eckhel to be fished for mostly with the harpoon, and are probably exposed 

 more or less to the influence of the surface current. Under these circumstances they must 

 very often be able to endure a degree of cold during the winter, and an amount of change 

 in the density of the water, for which it becomes difficult to account, even taking into 

 consideration the inferior quality of their skeletons. It is possible, however, that the 

 water of the northern part of the Black Sea may not affect the temperature of the 

 southern part to such an extent as would at first sight appear j^i'obable, and that, not- 

 withstanding the lower temperature of the northern shores, the general temperature of 

 the surface water during the winter immediately east and west of the Bosphorus may 

 not fiill below 55° as a minimum. The average of the aerial winter temperature of Con- 

 stantinople, according to Berghaus' map, is about 40°. 6, but this does not agree closely with 

 the lowest temj^erature recorded by Admiral Smyth of 53°. 4. It does not seem probable 

 that this comparatively high average winter temperature could be maintained if the waters 

 of the Black Sea and Sea of Marmora were to become very cold in winter, but it is a much 

 lower temperature than is found on the Algerine coast. The aerial isochryme, however, is 

 as low as 42". 5, according to Schouw's map. 



The northern shore of the ^gean Sea and the eastern shore of the Adriatic Sea are 

 jjopulous with sponges, and yet the former throughout its whole extent, and the latter from 

 Ragusa to Istria, have nearly the same average winter temperature, and possess a colder 

 climate in winter than the coasts of southern Italy or Spain, where no SpongiiB exist. 

 Again, upon consulting the invaluable little Eckhelian pamphlet, we find that the sponges 

 correspond in quality to this climatic change. The sort found at the head of the JEgean 

 is said to be the Spongia officinalis alone, and to have a " heavy, hard, close, very hairy 

 skeleton, often containing slime," and it is farther added that it is not much liked, and is 



1 Encyclopedia Brittanica, ninth edition. 'Proc. Roy. Soc. Vol. xxi, No. 145, p. 387. 



