pkestdent's addrkss. 191 



devoted to tlie MoUiisca, with many coloured plates, and comprise the 

 Chitons, the Nudibranchs, and the Land Mollusca of the expedition. 



The Narrative of the "Three Cruises of the 'Blake' " (1877-1881), 

 as recorded by Alexander Agassiz, occupies 556 octavo pages, published 

 in two volumes, and forms one of the most interesting and best illustrated 

 works on deep-sea exploration that we have seen. Its geographical 

 area includes the whole Atlantic coast of America ; the shores of the 

 Gulf of Mexico, the West Indian Islands, and so much of the 

 Atlantic itself as bears iipon the ocean currents and especially the 

 great area of the Gulf Stream. To whatever group we turn, whether 

 to the Fish, the Mollusca, Echinoderms, or Crustacea, we find new 

 and interesting material to attract our attention, which even the 

 great series of volumes of the " Challenger" Reports do not surpass 

 in interest, perhaps because of their very greatness. 



Pleurotoniaria was one of the most remarkable genera dredged by the 

 "Blake." Four recent species (and 14 individuals) of the genus are 

 known. The history of the genus dates back to the Silurian age. To 

 the dredging of the "Hassler" and the "Blake" are due the only 

 knowledge yet acquired of its soft parts. Two species are found in 

 the West Indies, of which the finest is P. Adansoniana, from 200 

 fathoms. The shell is four inches in diameter, richly pearly within, 

 and ornamented with elegant red and brown colours externally. The 

 anal notch extends nearly half the length of the body-whorl. A 

 second species, less brilliant and with a shorter notch, is P. Qmyana, 

 also obtained by the "Blake." 



In 1865 I figured and noticed the discovery of a specimen of 

 Pleurotomaria Beyrichii (Hilgendorf), from Enoshima, Japan (Geol. 

 Mag. 1885, pp. 433-39, pi. xi. fig. 1). A much larger Pleurotomaria 

 shell, indeed the second largest of living specimens,^ was brought 

 from Tobago, in the West Indies, in 1891, by my friend Mr. R. J. 

 Lechmere Guppy, of Port-of- Spain, Trinidad, and referred to Pleuro- 

 tomaria Adansoniana (Proc. Zool. Soc. 1891, Nov. 3, pp. 484-85), alt. 

 150, diam. 160, length of fissure 220 mm. Although no fewer than 

 1 1 60 species have been described, four only out of this number survive 

 at the present day, as widely separated geographically as the East 

 and West Indies and Japan. 



" Old-fashioned animals," tVrites Alexander Agassiz, "like Trigonia, 

 Limidus, and Lingula, are all from shallow ivater " [op. cit. vol. i. 

 p. 156). Further on he adds : " That none of the pala?ozoic forms 

 are found in the deep sea, seems to indicate, as has been suggested by 

 Moseley, that its first inhabitants date back no further than the 

 Cretaceous period.'" This appears to me' to be a powerful argument 

 against the absolute permanence of ocean-basins; for if the deep-sea 

 forms met with, and which must be the most ancient survivors, 

 have only a Cretaceous facies, then it is fair to infer that the 

 deep-sea areas of pre-Cretaceous times must have been elevated 

 subsequently, and their faunas destroyed. "Of course," he adds, 



* The largest is P. BKmphii, said to be 170 mm. high, by 190 mm. in diameter. 



