112 PUOCEEDINGS OF THE MALACOLOfilCAL SOCIETY. 



to Lit. 36° N. on the eastern side, are far less numerous at the same 

 latitude on the western. Santa Barbara, in 35'5° N. lat., shows few 

 traces of a tropical fauna. The surface temperature of the sea-water 

 at Cape Hatteras in August is 77° F., in February 68° F. (mean 

 72^° F.) ; the corresponding temperatures at Sta. Barbara are 66° F. 

 and 59° F. (mean 62^° F.) ; in other words, the February temperature 

 on the east coast exceeds the August temperature on the west on the 

 same parallel. 



These special conditions enable the temperate fauna of Upper 

 California to penetrate far southward ; Priene creffonensis, Redf., 

 e.g., has been found at Monterey, several of the Chlorostoma group at 

 Margarita Bay, in lat. 24° N., Purpxira ostrina, Gld., at the same 

 place. Closer investigation of the fauna of Lower California is much 

 to be desired, but one interesting fact is plain, that the great Gulf of 

 California, nearly 900 miles in length, forms a great hot-water basin 

 and is quite unaffected by the ocean currents. The result is that it 

 bears a tropical fauna up to its extreme northern point, so that the 

 Californian peninsula, more particularly in its northern portion, has 

 a tropical fauna on its eastern side, and a mixed tropical and sub- 

 tropical fauna on its western, and at certain points these two fauna 

 are within 50 to 60 miles of one another across the isthmus. The 

 mean annual surface temperature of the water inside the gulf is 

 somewhere near 80"^ F., on the outside it is about 72^ F. 



It may be remarked parentlietically that the Ked Sea and the 

 Persian Gulf offer similar examples of enclosed seas whose surface 

 temperature is very high. That of the lower portion of the Red Sea 

 rises to 90° F. in the summer, and that of the Persian Gulf to the 

 astonishing figure of 95° F. The heat of the lied Sea explains whj' 

 at Suez we have tropical forms such as Pyrula, Strombus, Murex 

 (typical), and Nerita living on the shore, in a latitude well to the 

 north of the Canaries. The liead of the Persian Gulf is in exactly 

 the same latitude as Suez. 



Now to come a little nearer home. On tlie eastern shores of the 

 Atlantic many southern species enjoy a wide range northward, and 

 many northern species an equally wide range southward. This is 

 due to the extremely equable temperature of the surface-water of the 

 sea from Norway to Morocco. Along this vast stretch of coast 

 there is no pronounced equatorial current moving northwards to bar 

 back the northern species, still less is there any polar current sweeping 

 southward along the coast to check the spread of the southern species. 

 It is quite true that the Gulf Stream and Antillean Current exercise 

 a powerful influence upon the temperature of our northern waters, 

 but that influence is so widely diffused, and the changes it induces 

 are so gradual, that at no point is there any sudden variation in 

 temperature, such as is found on the western side of the Atlantic. 

 Even the south-western shores of Nova Zembla (N. lat. 72°) are 

 washed in August by water no colder than 40° F. 



The isothermal line of 50° in August all but touches the North 

 Cape ; the isotherm of 60° in the same month is not reached till 

 south of the Wash, on the east of England, and Lough Swilh', to 



