The Terrestrial Mollusca Inhabiting the Cook's or Harvey Islands. 



By Andrew Garrett. 



The Cook's or Harvey Islands are embraced in an area between 157° and 160° 

 W. Long., and between 18° 40' and 22° 20' S. Lat. Their distance from the near- 

 est point of the Society Islands is about 480 miles to. the southward and westward, 

 and 640 miles southeast of Samoa. 



They comprise seven islands, mostly of small size, three of which are still virgin 

 grounds to the shell collector. Rarotonga, Atiu, Aitutaki, and Mangaia, from 

 whence all the known species have been derived, are, excepting the former, only 

 partially explored. Rarotonga, which is the largest and most lofty island, has 

 yielded a far greater percentage of species, simply because it has been much more 

 thoroughly explored than the others. 



The earliest known species were collected by Dr. Dean, during a cruise through 

 the group in 1861, when he discovered Helix fratercula and Omphalotropis ovata, 

 and obtained many examples oi Partula hyalina on Mangaia. In 1865 I visited 

 Aitutaki, Atiu, Mangaia, and Rarotonga, and found many new species, all of 

 which were forwarded to the late Mr. Pease for description. In 1869 I again 

 visited Rarotonga, and devoted six months to the investigation of its natural his- 

 tory, and discovered a number of new species, which have been described and fig- 

 ured in the Proceedings of the Academy of Natural Sciences of Philadelphia. 



GENUS MICROCYSTIS, Beck. 



M. EXCRESCENS, Mousson. 



Nanina excresceiis {Microcystis), Mousson, Journ. de Conch., 1870, p. 115, PI. T, fig. 5; 1811, p. 



8. Paetel, Cat. Conch., p. 84. 

 Nanina excrescens, Schmeltz, Cat. Mus. Godeff., v. p. 91. 

 Ee,lix excrescens, Pfeiffer, Mon. Hel., vii. p. 67. 

 Nanina subexcrescens, Garr. MS. 



I gathered nearly one hundred examples of this small species at Rarotonga, 

 where they occurred under damp, rotten wood and beneath moist, decaying leaves 

 on the side of inland ravines. 



Prof. Mousson's type specimens were found by Dr. Graffe in the Viti Islands, 



and he subseque^tly discovered it in the Tonga Group. 



(381) 



