GASTEROPODA. HELICIDZ. 83 
Synopsis Generum. 
Peritrema tenuiter marginatum, postice for- 
titer inchoatum. Umbilicus perforatus 35. BALma. 
Peritrema perfectum, marginatum, reflexum. 
Unmbilicus canaliculatus.............. 36. CLAUSILIA. 
Genus 35. BAL@maA. 
Testa valdé elongato-conica ; ad apicem extremum subobtu- 
siuscula. Apertura breviter semiovalis. Peritrema tenuiter 
marginatum, posticé fortiter inchoatum. Umbilicus perforatus. 
Operculum nullum. ‘‘ Tentacula brevia, subclavata.”’ 
Shell very elongately-conic ; its extreme apex rather obtuse. 
Aperture short-semioval. Peritreme slightly margined, strongly 
commenced behind. Umbilicus perforate. Operculum none. 
*Tentacula short, somewhat clavate.” 
Two European species only have yet been observed. I have 
two exotic species, which were communicated to me by Captain 
Carmichael, who found them amongst the elevated rocks of 
Tristan d’ Acunha. 
BALZ#A FRAGILIS. 
B. testa apertura posticé ad sinistram 1-plicata, anfractibus 
transversim elevato-striatis. 
Turbo perversus, Mont. Test. Brit. 355. t. 11. fig. 12; Penn. 
Brit. Zool. iv. 1302; M. & R. Trans. Linn. Soc. iv. 130; 
Dill. Desc. Cat. 876; Turt. Conch. Dict. 226. 
Pupa fragilis, Drap. Hist. des Moll. 68. pl. 4. fig. 4. 
Clausilia fragilis, Féruss. Ess. dune Méth. Conch. 51. 
Odostomia perversa, Flem. Edinb. Encyel. vii. 76. 
Habitat in arborum truncis et in fissuris rupium, satis frequens. 
Hinder part of the aperture of the shell on the left side, with 
one elevated fold; whorls with transversely-elevated strize. 
Although Balea fragilis is tolerably common on the trunks 
of trees, it is rarely found with a perfectly formed aperture to 
its shell. In the perfect state it may be generally taken, in no 
inconsiderable numbers, in the crevices of the loose rock, at 
the base of Arthur’s Seat, a little to the north of the basaltic 
