492 HYATT'S REVISION OF THE 



usually fished with the harpoon. The same species exists also alone at corresponding 

 localities along the shore of the Adriatic, and at the extreme locality, the Island of Istria 

 upon the limit of its distribution, it is said to be very rare, the form to be ugly, the skele- 

 ton hard, the color dark. Farther south, along the Dalmatian coast, it becomes abundant, 

 finer in texture and of a lighter color, but it is still inferior to the more southern or Levan- 

 tine variety. In considering such classes of facts, it must also be borne in mind that the 

 habitat of a certain sort or variety may largely determine the quality of the skeleton, even 

 where the temperature may be very favorable. Thus to the south of Quarnero, among the 

 islands, a much better quality of Spongia officinalis occurs than in the milder sea about the 

 Ionian Islands, which, as Eckhel remarks, is probably attributable to the slimy character of 

 the bottom. 



A sufficient reason for the absence of the Spongio3 on the Italian shore can be found 

 in its physical characteristics. The Adriatic is a comparatively shallow sea, and according to 

 Admiral Smyth's soundings, the greatest depth between Istria and Venice is 20 fathoms, and 

 in the centre of the sea to the southward, only 500 fathoms. A constant current from the 

 south passes northward along the eastern, and southward on the western shore. It is clear 

 and probably warm in its passage north during the winter from the south, and it seems 

 probable that this current parts with much of its heat in the shallower waters of the Gulf 

 of Venice, falling, perhaps, to a temperature which would prohibit the extension of the 

 Spongioe beyond Trieste. For if we apply Admiral Smyth's rule to the correction of the 

 average winter temperature for all these more northern localities, the Sea of Marmora, the 

 northern shore of the ^gean and Gulf of Venice, we find that the average temperature 

 of the water for these places would be represented by 56°. 5 + 1°.5 = 58°. But the isochryme 

 of 42°. 5 passes directly through the Sea of Marmora, the northern part of the ^gean and 

 Ragusa, leaving Istria considerably to the north with an isochryme of about .39°. 



It does not seem at all probable that any species of the true Spongiaj can live in surface 

 water which is affected for any length of time by such a degree of cold, and the only 

 explanation to be offi^red of their existence at such northerly points as Istria, must lie in 

 the warmth of the current from the south. If this is taken into consideration, and it is 

 also observed in the table how great the variation is between the air and water during 

 the winter season on the coast of Syrtis, the water being fully 16° wai'mer than the air ; 

 and how great the variation is also in summer, when the difference is sometimes 10°, as 

 noted by Dr. Carpenter, the air being 90° and the sea 80° ; it becomes evident that the 

 Avater of the Mediterranean, like that of other seas, responds very slowly to extreme 

 changes of temperature. The Adriatic current alluded to not only probably retains a 

 large part of its original temperature in its progress along the coast of Albania and 

 ■ Dalmatia, but even at Istria we should expect to find at least 15° difference between 

 the extreme isochrymal of the air and that of the water. If this is correct we should 

 reach the temperature of 39° + 15° = 54° as an isochr^anal at Istria, and 42°. 8 

 + 15° = 57°. 8 as the probable isochrymal of the water at Ragusa. A similar result 

 can be obtained also from the extreme aerial isochrymal of the Sea of Marmora, if it 

 is worthwhile to make a calculation in such a peculiar locality, namely, 42°. 5 + 10° = 52°. 5, 

 as an isochrymal for the Avater. These being the most northerly or most unfavorable points 

 at which the Spongife are known to exist, we cannot be far wrong in assuming from the 

 facts and inferences above cited, that in a comparatively quiet, clear sea Uke the Mediter- 



