PSEUDAMUSIUM FIBEILLOSUM. 107 



Specific Characters. — Shell below medium size, ovate, slightly oblique, the left 

 valve a little more convex than the right valve. The anterior margin cut away 

 under the anterior ear, descending outwards and downwards with a slightly 

 concave curvature till it meets the convexity which is continued round the Lower 

 margin, making a rounded obtuse angle ; the posterior margin rapidly approaching 

 the umbo, forming a well-marked ridge which limits the posterior ear. The ears 

 depressed, small, triangular, the posterior smaller than the anterior. Byssal notch 

 deep. Hinge-line short and straight. The umbones small, pointed, sub-central. 



Interior. — Unknown. 



Exterior. — The right valve is marked with irregular fine or coarse concentric 

 lines and stria' of growth, radiating striae obsolete. Ears apparently smooth. The 

 left valve is ornamented with many fine, close, irregular, radiating, fibrillose stria 1 , 

 crossed by concentric lines and rugae of growth. Ears with fine radiating striae. 

 Periostracum thick, often wrinkled, probably from pressure. 



Dimensions. — PL XVI, fig. 22, a right valve, measures — 



Antero-posteriorl v . . . .25 mm. 



Dorso-ventrally .... 25 mm. 



Localities. — England: Coal Measures, 150 yards over Great Mine Coal, river 

 at Ashton-under-Lyne ; above the Gin Mine Coal, Nettlebank Sinking, Small- 

 thorne, North Staffordshire; marine bed in Middle Coal Measures, River Tamo. 

 Dukinfield ; Pendleside Series, Leek and Waterhouses Railway, Staffordshire ; and 

 at Holder) and Pendle Hill, Lancashire. Ireland : (?) Coal Measures, Slieve Carna, 

 co. Mayo. 



Observations. — This species was established by Salter for some shells found in 

 the banks of the river Tame, at Ashton-under-Lyne. The series of shells used for 

 description and illustration are preserved in the collection of the Geological Survey, 

 Jermyn Street, and I have been permitted to study them. The illustrations are 

 somewhat hypothetical, as the right valve in well-preserved specimens is free from 

 radiating striae, and in full-grown specimens, where the periostracum is very thick, 

 they are not always seen in the left valve. The narrow hinge-line and small ears, 

 of which the anterior is larger than the posterior, are, however, correctly indicated. 

 I have met with this species in a much finer condition in beds of the Pendleside 

 Series at Holden, Bolland, and have referred the shell in lists of fossils to 

 Pecten praetenuis, von Koenen. I have arrived at the conclusion that this species is 

 identical with Salter's shell, and placed the name as a synonym of Vseudamusiwm 

 fibrillosum. Wolterstorff has given some good figures of the species, referring it to 

 von Koenen's Pecten prgeteiw is. 



It is of interest to note that P.fibrilloswm is found in the Pendleside Series and 

 Coal Measures of England and Ireland, and in the Culm beds of Herborn and 

 Magdeburg, one of several species common to these localities, and indicating a 



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