NORTH AMERICAN PORIFER^. PART II. 497 



83°, 86° at Suez. These great heats are also occasionally reached on the coast of Florida ; 

 at Punta Rossa and also at Key West, it is sometimes 90° or 92°. 



Capt. Pullen's ^ soundings give remarkably low temperatures for the depths of the Red 

 Sea, 44° at 1889 flxth., surface 81°. 5 ; 43°. 5 at 1500 fath., surfece 82° ; 45° at 1200 fath. with 

 surface 81°. 5. The northex-n part of the Red Sea, where, according to Von Eckhel, most 

 of the commercial sponges are found, has an aqueous isochrymal of about 70°, and this ac- 

 cords with Carpenter's remark in the work above quoted, that the waters of the Red Sea 

 are uniformly 71°, but not wholly, since he has inferred that this is the mean temperature 

 at all dej)ths, which cannot jDOssibly be the case unless all other observers are in error. 



The sponges of the Red Sea, according to Von Eckhel, are inferior to, and rarer than, 

 those of the Mediterranean ; he compares them to the Zimocca variety, describing the skel- 

 eton as brittle, entirely red, and very dark at the base. Not having seen any speci- 

 mens unquestionably from this locality, I cannot compare them with the Key West and 

 Australian varieties ; but they are evidently, so far as quality is concerned, more like the 

 coarser Zimocca sponges of the Mediterranean, since Eckhel describes them as mixed with 

 these in the trade. The extremely hot temperature of the Red Sea does not, therefore, 

 when acting in perfectly clear water, produce so great changes as when the waters are more 

 loaded with sediment, as in the shallows of the Florida coast, or else these specimens could 

 not be sold commercially even in the company of the inferior Mediterranean qualities. 



I have seen but few true Spongias from Australia. These are coarser than their 

 congeneric form, Spongia discus, and, like this species, have an excessively dark, I'ough 

 skeleton. The neighborhood of Sydney, where they were collected, lies under the marine 

 isochrymal of 62°, as laid down by Dana, and the coast is open and apparently unfavor- 

 able for the growth of the commercial sorts. This, and the aspect of the specimens, leads 

 me to think that they were beach specimens which had drifted from the coast of Queens- 

 land, which, judging from the descriptions of voyagers, must be exceeding favorable, inside 

 of the great boundary reef, for the growth of the true Spongite. The collection of the 

 Keratosa received from Dr. Farlow, Avas made at Port Phillip, near Melbourne, on the 

 south coast of Australia, and though the genera are well represented, there are among 

 them only three specimens allied to true Spongiaj ; these have coarse, loosely constructed 

 skeletons, and I have been obliged to propose a new generic name, Oarterosjjonr/ia. 



Although the distribution of the Spongias is not limited by the same isochrymal as that 

 demonstrated for the reef building corals by Prof. Dana, namely, 68°, the association of these 

 with the Spongite having coarse and inferior skeletons cannot be a matter of accident. The 

 coral reefs afford good holding ground for the bases of the colonies and protection from the 

 excessive surf of ocean shores, v/hile they grow in water, the remarkable clearness of which 

 to a considerable depth is the constant subject of remark. These are undoubtedly 

 favorable conditions, since they are common also to the Mediterranean waters. The 

 great quantity of calcareous sediment, however, which is churned by the waves in 

 the winter on the borders of a coral reef, is not present in the Mediterranean ; and 

 the average temperature, also, which is very much higher than that under which the 

 finest sponge skeletons are produced in the Mediterranean, cannot be considered as 



* Trans. Bombay Geogr. Soc. Vol. xiv, p. 44, 1859. 



MEMOIRS BOST. SOC. NAT. BIST. VOL. II. 125 



