102 CARBONIFEROUS LAMELLIBRANCHIATA. 



Exterior. — The surface is ornamented by a few distant, concentric, acute ridges, 

 not quite so well marked in the right valve, separated by broad, concave, concentric, 

 smooth grooves. The ridges pass on to the ears, the contour of which they follow. 

 Very obscure radiating striae are at times seen crossing the grooves. 



Dimensions. — PL XVI, fig. 28, a left valve from Cork, measures — 



Antero-posteriorly . . . .18 mm. 



Dorso-ventrally . . . .24 mm. 



Localities. — England : the Carboniferous Limestone of Narrowdale, North 

 Staffordshire ; Park Hill, Derbyshire. Ireland : the Carboniferous Limestone of 

 Cork and Little Island, co. Cork. 



Observations. — This very characteristic shell is rare, but Mr. Joseph Wright's 

 cabinet contains five specimens, one of which is a bivalved example, though 

 unfortunately not perfect in the neighbourhood of the ears. It shows the left valve 

 to overlap the right valve considerably, and to be much more convex than the 

 latter. The concentric folds are triangular in section, and not rounded as in 

 I'sciitlamusium auriculatum. 



<, 'mas 1'sKUDAMUSiUM, H. and A. Adams, after Klein, 1858; emend Verrill, 18 ( J7. 



Pseudamusium, Klein, 1753. 



H. and A. Adams (pars), 1858. 



Verrill, 1897. Trans. Connecticut Acad., vol. x, p. 60. 



Generic Characters. — Shells nearly equal, the right flatter than the left, ovate 

 or subcircular ; margins simple. Ears well defined, small, straight, obtuse-angled. 

 Exterior smooth, or with lightly marked radiating striae or grooves. 



Observations. — Prof. Verrill has given a long account of this genus and its 

 limitations in his paper on "A Study of the Family Pectinidx " above cited, and it 

 is unnecessary to refer much to the synonymy here. The distribution, according 

 to him, is Recent to Cretaceous. This genus is more closely allied to Oamptonectes, 

 Meek, most of the species of which are Mesozoic. Prof. Verrill remarks that the 

 Latter " is generally regarded as only a section of Pseudamasiwni." At any rate 

 the relationship between the two genera is so close that it would be impossible to 

 decide to which the Carboniferous examples might the more appropriately be 

 referred. 1 have therefore adopted that genus which has the right of priority. 



