184 CARBONIFEROUS LAMELLIBRANCHIATA. 



obtuse angle, and separated from each other below the umbo by a very small 

 cavity for the internal cartilage. The teeth in the posterior portion are small 

 and numerous (20) ; those in the anterior part few (5) and moderately large. 



Exterior. — The shell is almost smooth, but under the microscope it is seen to 

 be ornamented with very fine, regular, close lines of growth. 



Dimensions. — The type-specimen in the Portlock Collection (PL XV, fig. 32) 

 measures — 



Antero-posteriorly. Dorso-ventrally. From side to side. 

 17 mm. 11 mm. — 



Another specimen "> _, _ H 



(Fig. 34, PI. XV). j 15mm - 10mm ' 7mm ' 



Localities. — England : the Redesdale Ironstone, Northumberland. Below the 

 base of the third bed of Millstone-grit, Congleton Edge, Cheshire ; over the 

 Great Mine Coal, Ashton-under-Lyme. Scotland : Upper Limestone series : 

 Linn Spout, Dairy; Orchard. Lower Limestone series: Lickprivick, East 

 Kilbride ; Horizon of Hurlet Limestone, Wilkieston, Fifeshire. Ireland : Armagh 

 and Tyrone ; in shale at Benburb. 



Observations. — The type specimen of Portlock's N. Isevirostrum is fortunately 

 preserved in the Museum of the Geological Survey, Jermyn Street, and I am 

 permitted to refigure it by the kindness of the authorities (fig. 32, PL XV). The 

 fossil is much compressed, but still the peculiar contour is well preserved. 

 Portlock draws attention to the peculiar upward curve of the lower border 

 posteriorly. The original of M' Coy's Nucula longirostris is preserved in the 

 Griffith Collection in the Museum of Science and Art, Dublin. In the description 

 M'Coy mistakes the anterior for the posterior end. It runs thus : — " Transversely 

 clavate j width two and a half times the length ; anterior side produced into a 

 very long narrow beak, abruptly truncated at the end ; posterior side moderate, 

 rounded ; surface very finely striated transversely." There seems to be some very 

 considerable discrepancy between this description and the figure to which it is 

 said to refer. The actual measurements of the figure are 17 mm. transversely 

 by 10 mm. from umbo to lower border, which does not agree with " width two 

 and a half times the length ; " neither can the posterior border be said to be 

 " produced into a very long narrow beak." On the contrary, the posterior end is 

 far less produced than in other species of the genus. 



I believe that the figures and descriptions of N. longirostris and N. clavata 

 have been accidentally substituted for one another; and that the figure named 

 N. clavata refers to the description of N. longirostris, and vice versa. I may say 

 that the names on the type specimens in the Dublin Museum are in accordance 

 with this view, being exactly the reverse of those on the plate in M'Coy's work. 



Neither of these names, however, will stand, the shell figured as N. clavata 



