CUCULL^A. 59 



and G. fibrosa have been considered by Briart and Cornet, Pictet and Campiche, 

 Pictet and Renevier, Downes, and others, to belong to the same species. Sowerby's 

 glabra was a more rhomboidal example than his fibrosa, but a large series of 

 specimens shows that there is no essential difference between the two. 



One of the specimens figured by Goldfuss (fig. 1 c) as Area glabra 

 (Sowerby) was regarded by d'Orbigny as distinct from the others (figs. 1 a, b, d), 

 and named l by him Area subglabra. This name has been since generally adopted 

 for the form found in the Aachen Greensand (Senonian). Goldfuss does not state 

 from whence his figured specimens came, but gives in the text, as localities of the 

 species, Quedlinburg, Coesfeld, Aachen, Kelheim, and Blackdown. J. Bohm 2 

 found, in the Museum of the Schloss Popplesdorf, examples labelled " England" 

 which agree well with Goldfuss' figures, and he believes that the figured 

 specimens really came from Blackdown, and are the true Gucullma glabra, 

 Sowerby. Briart and Cornet 3 also regard Goldfuss' glabra as identical with 

 Sowerby's. The Blackdown specimens of G. glabra, Sowerby, certainly agree 

 closely with the figures of Goldfuss (except fig. 1 c, in which the lateral teeth are not 

 parallel to the hinge-margin, but this may have been a worn specimen) ; speci- 

 mens and. figures both differ considerably from the figures of the undoubted 

 Aachen form given by Holzapfel ; 4 the last-named author, however, does not 

 appear to accept Bohm's view, but takes the glabra of Goldfuss as the type of 

 Area subglabra, d'Orbigny. 



Judging from Holzapfel' s figures and description, Gucullsea subglabra of 

 the Aachen Greensand differs from G. glabra, Sowerby, in the shell being more 

 convex and relatively higher ; the hinge-line relatively shorter ; the lateral teeth 

 shorter, somewhat curved and not quite parallel to the hinge-line ; the absence 

 or indistinct nature of the radial ribs; and perhaps also in the less distinct carina. 



The arrangement of the teeth in G. glabra is similar to that in G. Mullen, 

 Holzapfel, 5 from the Aachen Greensand; but in that form the shell- is more 

 rounded than in G. glabra, it is without a keel, the area is smaller, the hinge-line 

 shorter, &c. 



G. Mailleana (d'Orbigny) (see p. 63) is relatively longer, more oblique — owing 

 to the greater proportionate length of the posterior margin, and is ornamented with 

 well- marked concentric grooves, the radial ribs being absent or indistinct. 



1 ' Prodr. de Pal.,' vol. ii (1850), p. 244. 



" "Der Grunsand von Aachen und seine Molluskenfauna," ' Verhandl. des naturh. Vereines der 

 preussisch. Kheinl.,' &c, vol. xliv (1885), p. 92. 



3 " Descript. de la Meule de Bracqueguies," 'Mem. Cour. et Mem. dea Sav. ctrangers, Acad. 

 Koy. Belg.,' vol. xxxiv (1868), p. 55. 



4 " Die Mollusken der Aachener Kreide " (' Paheontograpliica,' vol. xxxv, 1889), p. 20G, pi. xxii, 

 iiga. 3, 5. 



5 Ibid., vol. xxv (18S9), p. 209, pi. xxiii, fig. 1. 



