COOKE : DISTRIBUTION OF PURPURA LAPILLUS. 203 



months. Its southward range is equally restricted by the influence 

 of warm-water currents flowing northward from the Gulf of Mexico, 

 and possibly also by the fact that south of Long Island tlie shore 

 appears not very suitable for species requiring rocky lodgment. 



That P. lapillus should be able to exist up to N. lat. 69° in 

 Greenland, and unable to exist further north than about 51° in 

 Labrador, is at first sight very remarkable, for, in other words, it 

 occurs on the east of Davis Strait more than 1,200 miles north of its 

 most northerly point on the west of that strait. But the western 

 coast of Greenland has its climate softened by the influence of a warm 

 southern drift from the Atlantic, which makes itself felt as far north 

 as Baffin's Bay, and renders liuman liabitatiou possible. The eastern 

 shores of Greenland are swept by the ice-bearing Greenland current, 

 flowing direct from the Polar basin. 



Note on the Northern Group of West American Purpura. 



This group exhibits, perhaps more tlian any other section of the 

 genus, the tendency of Purpura to vary in shape, size, and sculpture. 

 Some writers, e.g. Hemphill (Williamson 126), regard all these forms 

 as mere varieties of P. lapillus. But P. P. Carpenter (14, p. 148) 

 long ago sufficiently distinguished the three species under which the 

 different forms must fall, and more recent authors, e.g. Taylor (115) 

 and Vanatta (118), agree with him in essentials. 



Thus we have (only a selection from the synonymy is given) — 



1. lima, Martyn, 1784, Univ. Conch., ii, tig. 46 (Buccinwn). 



= canaliculata, Duel., 1832, Ann. Sci. Nat., xxvi, p. 104, 



pl- i, fig- 1- , . 



= decemcostata, Midd., 1849, Beitrage Malac. Iloss., pts. ii, iii, 



p. 116, pi. ix, figs. 1-3. 

 + var. attenuata. Reeve, 1846, Conch. Icon., sp. 49, pi. x, fig. 49. 

 + var. analoga, Forbes, 1850, P.Z.S., xviii, p. 273, pi. xi, fig. 12. 



2. plicata, Martyn, 1784, Univ. Conch., ii, fig. 44 {Buccinum). 



= lamellosa, Gmelin, 1790, Systema, p. 3498, No. 173 

 {Buccimmi). 



— crispata, Chem., 1795, Conch. Cab., xi, pp. 84-5, 



pi. clxxxvii, figs. 1802-3 [Buccimim). 



— ferruginea, Esch., 1829, Zool. Atlas, pt. ii, p. 10, pi. ix, 



fig. 2a-h {Murex). 

 -f- var. lactuca, Esch., 1829, Zool. Atlas, pt. ii, pi. ix, fig. Za-h 



(Murex). 

 + var. septe7itrionalis, Reeve, 1846, Conch. Icon., sp. 50, pi. x, 



fig. 50. 



3. emarginata, Desh., 1839, Rev. Zool., p. 360; Mag. Zool., ser. ii, i 



(Moll.), pi. XXV, 2 figs., 1839. 

 = conradi, Nutt. MSS. 

 = lapillus, Cooper (iion Linue). 

 + xar. fuscata, Forbes, 1850, P.Z.S., xviii, p. 274, pi. xi, fig. 13. 



=» saxicola, auctt. {non Val.). 

 + var. ostrina, Gould, 1852, Otia, p. 225 = Moll. U.S. Expl. 

 Exped., AVilkes, xii, p. 244, fig. 310. 



