12 
but it is too flat and lin^ulilbrm to be intimabdy compared with that species. 
'Jdiis is au exceedingly })lentiful shell at Bowral, and in company Avitli h'. 
Jiotnv/le/m.s enters extensively into the formation of the ironstone hands at 
that locality. 
Local ////. — Railway cutting near Gibraltar Tunnel, Bowral, Co. Camden. 
Jlorizo )/. — Ironstone hands in the AVianamatta shale. 
CoUcclor, — Mr. R. Dunstan, after whom I have much pleasure in 
naming this interesting species. 
Geniis UNIONELLA, (jen. hoc. 
Gen. Char . — Shell (juadraiigular to irregularly trapeziform, cquivalve, 
inequilateral ; umhones depressed and contiguous, eroded ; ligament 
external ; cardinal teeth appai-ently one in each valve ; no lateral teeth ; 
anterior adductor impression single, hounded posteriorly by an oblique ridge ; 
posterior adductor impression single and inconspicuous ; supplementary 
umhonal muscular scars pit-like, cither forming a semicircular line, or 
clustered ; pallial line simple. 
Ohs . — This genus has been instituted for the reception of small bivalves 
collected by Mr. B. Dunstan at Bowral. The undoubtedly eroded condition 
of the umhones indicates either the Unionidae or the Cyrenidie as their natural 
resting-place ; but Avith no genus in either of these families do they otherwise 
seem to agree. The single condition of the adductor muscular impression, 
and the faintly marked state of the ])osterior clearly separate the present shells 
from Unio, to which they are again, hoAvever, related through the umhonal 
muscular scars, and the exterior ligament. The absence of lateral teeth, which 
I believe do not exist in the present genus, shows a transition toAvards 
Anodonta ; but there are no other characters in common. Unfortunately for 
classilicatory purposes, the acknoAvledgcd genera of the Unionidae are 
established on such limited characters as to render them practically useless, 
especially Avhen such minute questions as generic comparison are entered on. 
The hinge structure, although not AA'holly knoAvn, is still sufficiently 
apparent to separate Vnlonella, from any of the Cyrenidae. I have not been 
able to act ually isolate a hinge line, but in numerous cases Avhere the umhones 
have been dissolved, and the anterior end of the shell decorticated, Ave are 
