Mascarene Land-Mollusca. 433 



are two minute species under the names of Microcystis 

 barclayi and M. perlucida : the former I first compared witli 

 three examples in the Natural History Museum ; these were 

 originally in Henry Adams's collection and we may therefore 

 consider them typical. I was afterwards able to see the 

 typical specimens in the Benson collection at Cambridge, 

 through the kindness of Prof. S. F. Harmer. There are 

 many examples of barclayi, Bs., all from the Mauritius — 

 about nine are labelled Trochomorpha, two Erepta, one no 

 genus. Most of them are not fully grown and many aie 

 imperfect, particularly at the peristome — no doubt due to the 

 method adopted by McAndrew of sticking the shells on 

 cards, which lie among other cards. None of the specimens 

 come up to the size recorded by Benson, viz. 4 mm., the 

 largest being 3'25 mm. The sculpture of barclayi consists 

 of irregular fine close ribbing, showing stronger in some 

 specimens than in others and extending to the protoconch. 

 I give figures of one of the Cambridge Museum shells 

 (Pi. X. figs. 1-1 h), as I do not think the species ha^ever 

 been figured before; its principal character is the sub^igu- 

 late periphery : this specimen was 3 mm. in major diameter. 

 It is difiicult to understand why Von Martens, in the 1860 

 edition of * Die Heliceen,'' included a small shell like barclayi 

 in Erepta — a genus Albers created in 1850 — with type 

 stylodon, Pfr., a large solid shell. The sculpture of the 

 other shell found by M. Dupont is quite difterent from 

 barclayi and from all the other minute helices in the B.M. 

 collection examined by Mr. Edgar Smith and myself. 



As barclayi cannot be retained in the genus Erepta, I 

 place it with other similar small shells from these islands in 

 anew genus {Lonisia) of the Zonitidse (see PI. X. figs. 1-1 b). 



Genus Louisia. 



Shell small, subpyramidal or globose, last whorl keeled 

 or rounded on the periphery, with regular transverse distant 

 fine ribbing. Animal with a mucous gland and peripodial 

 groove. Ovoviviparous in habit. The radula with about 70 

 teeth in a row ; central teeth on broad plates, few in number, 

 all tricuspid ; marginals also tricuspid. Jaw oxygnathous. 



Louisia insularis, sp. n. (PI. X. figs. 2-2 t', Type.) 



Locality. Mauritius {E. Dupont). 



Shell depressedly globose; sculpture fine somewhat 

 regular ribbing, which on the last whorl extends to the 

 periphery and basal side; first whorl smooth ; colour ochra- 

 ceous; spii'e low, apex blunt ; suture well impressed ; 



