81 



Morcton Bay, Queensland, which is not the case. It appears 

 that young specimens of Unio cucumoides, which occurs there 

 rery much resemble our species. This is probably the origin 

 of the erroneous habitat in Reeve. It would be rather sin- 

 gular to find a Tasmanian species in a river on the Australian 

 continent more than 1,400 miles away, and in no intermediate 

 locality. 



PISIDIUM. Pfeiffer. 



(Systematische Anordnung und Beschreibung Deutscher Land imd 

 Wasserschnecken, &c., Cassel et BerUn 1821 — 28, 3 vols. 40.) 

 Testa toniis atpiivaliHS, i)ui'quilateraUs, antice pnxlucta, rpldennide 

 oUvaceo-cornca imluta, concentrice rugosa vet striata, intus albida, 

 nmbonibus promhientihus, tumidis, ligamentum suhexternum, incon- 

 spicmim, latere minore insertum ; dentibus cardinalibiis minimis, in 

 idrdque valva duobus diver gentibus, inuna valva binis, subdistantibus 

 snbelougaiis ; in altera (piatuor duobus vere exiguis ; impressionibus 

 muscidaribns duob^ls, lateralibus ; impressione pallii sinu nullo. 



Shell thin equivalve inequilateral, produced in front, covered 

 with an olive epidermis, concentrically rugose or striate, whitish 

 within, urabones pi'ominent, tumid, ligament subexternal, in- 

 conspicuous, inserted in the shorter side, with two small hinge 

 teeth in each valve, one of which is double in one valve, 

 lateral teeth distant and somewhat elongate, muscular im- 

 pressions two, with no pallial sinus. 



This genus was separated from Cyclas on account of the 

 dlflfereuce of the siphonic tubes, and of the shells which in 

 Pisidium are smaller, with the anterior side the longer, and 

 the ligament on the shorter side. 



They are found throughout Europe abundantly, but the 

 foreign species ai'e not well known, though India and New 

 Zealand both possess species. 



Pisidium tasmaxicum, n.s. P. testa orbicidato-ovata, tenuis, ventri- 

 cosa, pellucida, albida, regidariter concentrice striata, inquilatcralis, 

 ntrinque rotundata ; latere antico subproducto, postico obtuse rotundato, 

 umboitibns obtusis, ligament itm inconsjncuum. 



Shell ovate, thin, ventricose, pellucid, whitish, regularly con- 

 centrically striate, inequilateral, or rounded on both sides ; 

 anterior side subproduced, posterior rounded obtusely, umbones 

 obtuse, ligament inconspicuous. Length from 2 to 4 ; 

 breadth li- to 2^ ; height 1 to 2 mill. 



Habitat, Brown's Eiver, Great Lake, Lake Dulverton, 

 Dunrobin, and creeks near Hobarton. A small fragile shell in 

 which the epidermis is not easily discovered. The specimens 

 vai-y in size, and those from the Lakes are larger, a little more 

 oblong, with shades of smoky horn, but I have never seen 

 enough divergence of character to warrant the erection of 

 more than one species. 



