BY JOHN SHIRLEY, D.SC, F.M.S. 11 



stretch of deep sea parallel to, and west of the Andes, separat- 

 ing two very different conchological faunas. 



A study of the molluscs of the Pacific coast of Mexico 

 and Central America shows that 17 species known in Queens, 

 land also inhabit those distant waters. They are in some 

 cases of genera like Hipponix, Cheilea and lanthina, which, 

 from their mode of life, are easily and widely spread • 

 but include others such as Natica, Drupa (Ricinula), and 

 Pyrene (Columbella) which have no special means of dis- 

 persal in adult life. 



Of the barrier between the equatorial portions of the 

 Pacific and Atlantic formed by Central America and the 

 Isthmus of Panama, Geikie* says : — " While the fishes 

 and molluscs living in the seas on the two sides of the 

 Isthmus of Panama are on the whole very distinct, a few 

 shells and a large number of f shes are identical ; whence 

 the inference has been drawn that though a broad water- 

 channel originally separated Xorth and South America in 

 Miocene times, a series of elevations and subsidences has 

 since occurred, the most recent submersion having lasted 

 but a short time, allowing the passage of locomotive fishes 

 yet not admitting of much change in the stationary molluscs. 

 Of species found on the Atlantic side of America, in the 

 West Indies, Florida and Brazil, 35 are also found in 

 Queensland ; two of these are reported doubtfully, and 

 may be rejected ; the remainder include species of Fis- 

 surella, Hipponix, Litorina, Tectarius, Planaxis, Epigrus, 

 Bissoina, Litiopa, Cerithium, lanthina, Epitonium (Scalaria), 

 Cymatium (Triton), Distortrix, Septa (Triton), Cassis, Tonna 

 (Dolium), Trivia, Oliva, Murex, Hydatina and Pyrene 

 (Columbella). 



Geikie's use of the term " stationa,ry molluscs " is 

 rather misleading. It may be true that they deserve that 

 title in adult life, but the immature mollusc in the veliger 

 period is a great traveller, floating over widespread areas 

 before coming to rest. Many of these juvenile forms, 

 before their proper place in molluscan history was under- 

 stood, have been regarded as species, and given such names 

 as Macgillivrayia Sinusigera, etc. This power of ranging 



*Geikie, Text Book of Geology, I., 391. 



