152 CARBONIFEROUS LAMELLIBRANCHIATA. 



Transverse markings are almost obsolete, though occasionally here and there 

 some indications of these growth-lines may be traced. 



Dimensions. — PI. XI, fig. 4, the type specimen, measures — 



Antero-posteriorly . . . .49 mm. 



Dorso-ventrally . . . .21 mm. 



Laterally . . . . .22 mm. 



Localities. — Ireland : The Carboniferous Limestone of Garrahies, Co. Kerry ; 

 Townland of Cruicerdth, three and a quarter miles south-east of Drogheda, 

 Co. Meath ; Cregg and Nobber, Co. Meath ; in Yellow Sandstone at Bruckless. 



Observations. — This species, as far as I am aware, is confined to the 

 Carboniferous beds of Ireland, and was one of the forms described by M'Coy in 

 his early work (1844). I am fortunately able, by the kindness of the authorities, 

 to reproduce the figures of the original specimen (PL XI, fig. 4), now preserved 

 in the Griffith Collection, Dublin Museum of Science and Art. The other 

 specimens are in the Collection of the Geological Survey of Ireland, under the 

 same roof; and these I figure, PL XI, figs. 1, 2, and 3, through the kindness of 

 Sir A. Geikie. 



In the Supplement to his work on the ' Carboniferous Fossils of Belgium ' 

 (sup. cit.), de Koninck changed M'Coy's specific name to Area Maccoyana, in 

 order that the shell might not be confounded with Area tenuistriata of Miinster. 

 In his later work, however, de Koninck restores the name Parallelodon tenui stria, 

 but does not record the fact that his Area Maccoyana is a synonym. 



I very much doubt whether any of the shells figured in this later work are 

 correctly referred to the species under discussion, though the former figure is 

 evidently correctly placed as identical with Cucullxa tenuistria of M'Coy. All the 

 shells that de Koninck figures as P. tenuistriatus have numerous well-marked 

 concentric lines; in fact his description (p. 162) of the exterior is, " Surface 

 garnie de stries concentriques d'accroissement, croisees par des stries rayonnantes 

 nombreuses et peu distinctes." 



I should feel inclined to place all those shells that de Koninck refers to 

 P. tenuistria under P. Walciodorensis, to which species P. tenuistria, M'Coy, is 

 closely related in shape and size; the distinguishing features between the two 

 species being that in P. tenuistria the posterior end is much narrower dorso- 

 ventrally than the rest of the shell ; while in P. Walciodorensis this is not the case, 

 and in the latter species concentric striae are always present, and much contorted 

 in the line of the byssal sinus. 



For de Koninck's remarks (p. 162) on this species see above, page 150. I 

 am doubtful whether such small differences should be considered of sufficient 

 value for the erection of separate species ; but, as a reference to the figures of 

 P. Walciodorensis, PL X, figs. 11 — 15, P. tenuistria, PI. XI, figs. 1 — 4, will show, 



