NORTH AMERICAISr PORIFER^. PART II. 



495 



The finding o these specimens and the considerations above noted, induced me to apply 

 again for assistance to Gen. Myers, Chief Signal Officer, for the temperatures during the 

 months of January and February, at the stations along the Atlantic coast south of Cape 

 Hatteras. The records, which were immediately forwarded, and are in the accompanying 



TEMPERATURE OP WATER FROM OBSERVATIONS TAKEN AT BOTTOM. 



table, give the strongest support to the idea that the temperatui'e has probably more influ- 

 ence than any other cause in limiting the distribution of the Kerato.se sponges to the more 

 southern localities. The commercial qualities being in all cases .shallow-water animals could 

 not, without great difficulty, spread to the northward from the Key West region to the 

 region along the Atlantic coast of Florida ; they would be exposed after passing Jackson- 

 ville, not only to all the unfavorable conditions of the open sandy .shores, but also after 

 a few fortunate forms had gained the inlets, the general absence of favorable holding, and 

 perhaps feeding grounds, would be supplemented by an average temperature appi'oximat- 

 ing during the month of January to the unfavorable limits previou.sly traced in other local- 

 ities. North of Jacksonville the temperatui-e falls below 58° very rapidly, becoming very 

 unfavorable to the existence of these forms ; thus at Savannah it averages as low as 49°. 

 Here there is evidently some local disturbance, since the regular rate of decrease northward 

 would make this some degrees higher. At Charleston, the Januaiy temperature is only 

 51°, and at Wilmington, 46°. These averages, and the recorded isochrymals, are somewhat 

 remarkable confirmations of the deductions previou.sly made in the Mediterranean and 



