THE SESSTLE BARNACLES. 19 



Species. 



EasU^rn North Atlantic and Mediterranean '18 



Wenlern North Atlantic and Gulf of Mexico 11 



South Atlantic and Antarct ic 4 



West coai^t of South Ameritni 1 



Hawaiian Islands 1 



Southwestern Pacific (near Kermadcc and Gambier Islands) 2 



East. Indies (Malay Archijielago and Philippines to the Andamans) 13 



Twtal 50 



It will 1)C sect! by the abcn^e table thai (except in the North Pacific) 

 Vcrrucse are most abundant where the sea bottom has been most 

 assiduously exjdorod, that is, in the North Atlantic. The compara- 

 tiro scarcity of species in other seas may very likely turn out to be 

 due to the imperfection of oiu- knowledge. 



Wliile most deep-water Veri'ucse are now known from a single 

 station, the geographic distri])ution of species will, I think, eventually 

 prove to be somiewhat extended, v/here conditions favor; this opinion 

 being based upon the data relating to V. alha, the varying forms 

 under 1". calotheca, etc. The limits of their range seem to be deter- 

 mined by temperature, whicli of course is more or less closely corre- 

 lated with depth. Thus, V. alha, in its several varieties, has an 

 extension from Barbados to Ilatteras, yet always in bottom tempera- 

 tures of from 71°.3 to 75° F., and depths of 45 to 68 fathoms. V. 

 mlotlicca, with the two forms I have segregated as races, has an even 

 greater geographic extension, with a known range in temperatiu'e of 

 only from 45°. 6 to 48°.3 F. Whether the restriction to a naiTow 

 range of temperatures which seems indicated by the small number 

 of observations available be due to the direct effect of temperature 

 on the bamacle,^ or to indirect action through the food supply or 

 other factors, is uncertain. That they are so restricted accounts for 

 the emphatic specific diversity I have found to exist between the 

 warm-water Verrucie of our continental shelf and the species obtained 

 by European expeditions in the eastern Atlantic. 



In the group of V. darwini, hicornuia, and raiJihuniana, which live 

 in 1,550 to 1,769 fathoms, bottom temperature 37° to 38°.5 F., aVo 

 find very closely related species on the two sides of the North Atlantic 

 and as far south as the Antarctic Ocean. It seems likely that this 

 group of forms, living in the depths in temperatures approaching 



1 Seven of the eighteen eastern Atlantic species were briefly diagnosed by Aurivillius, witlioiit figures. 

 Until a more complete accoimt of these forms is given they can not be critically compared with really 

 known forms. Doctor Hook significantly remarks that " Aurivilliusand Gruvelhave described 10 different 

 species of I'lrrK^ca as orcurrmg near the Azores; between some of those the dilTercnces seem to 1)0 very 

 small." It seems curious that the Verruca; obtained near the Azores by the Travaillcur and Talisman 

 (de^scribed by Gruvcl) should a// be different from those dredged in the same waters by the Princcsse Alice 

 (described by .Vurivillius). 



2 Littoral and pelagic barnacles outside of the Tropics tolerate very considerable variations in 

 temperature. 



