7210 Mollusks, 



R. soliita. Mr. Webster has met with this species arnong some shell- 

 sand I sent him from Lamlash Bay, and Dr. Landsborough and Mr. 

 Bean had previously recorded it from the same locality. Bute, Bean. 

 *R. Ulvae [Cingula suhumhilicata). Common in the salt-water marsh 

 at Brodick. Examples taken there are commonly of a very curious 

 form. The whorls of the young shell are remarkably small ; they then 

 suddenly enlarge, and ultimately the small whorls of the upper portion 

 of the spire drop off, leaving an obtusely truncated apex, as in the 

 genus Truncatella. 



Jeffreysia opalina. Confined, as far as ray observations go, to the 

 Allans rock pool, where it is abundant, but always small. 



J. diaphana. In company with the last, and equally common in 

 that locality, but has not been met with elsewhere in the district. 



Skenea Planorbis {Skenea depressa). Very abundant. 



S. nitidissima. Frequent. Alive in rock pools at Clachland Point, 

 Arran ; and dead in dredged Lamlash Bay sand. 



S. Rota. Rare in sand from " Landsborough's Bay." 



S. divisa. Frequent in the same locality as the last. 



S. costulata. There is a specimen of this shell, which I have seen, 

 in the cabinet of Mr. Bean, who procured it from Lamlash Bay sand. 

 The genus Skenea in the ' British Mollusca " contains a motley assem- 

 blage of minute shells which had since proved to belong to widely 

 different genera, and, which, indeed, were only provisionally placed 

 by Forbes and Hanley together. Jeffreys and Messrs. Adams (in their 

 * Genera of Recent Mollusca ') would retain Planorbis as the sole 

 representative of the genus Skenea ; Messrs. Adams deposit the 

 remaining species in the genus Cyclostrema, Marryatt, among the 

 Trochidse, while Jeffreys places Culteriana, costulata (?), laevis (?) 

 and divisa in Margarita, among the Trochidae, and has constituted 

 a genus Omalogyra for the reception of nitidissima and Rota: he 

 leaves this genus among the Littorinidse. Clark unites Planorbis 

 to the genus Rissoa, places Culteriana, divisa, costulata and laevis in 

 Trochus, nitidissima in Truncatella, and " believes " that Rota is 

 the young of Caecum Trachea. The utmost that can as yet be con- 

 sidered satisfactorily determined is that Planorbis should remain in 

 the family as it is, and that Culteriana and divisa must be removed to 

 the Trochidse ; all the rest is conjecture, or at least has no sufficient 

 proof. 



Fam. IX. Turritellid(B. 

 *Turritella communis {Turritella Terehra). Not common. 



Caecum glabrum {Brochus glaher, B. arcuaius). Alive in rock 



