76 DEVONIAN FAUNA. 



Under the same name Sandberger^ figures a large group of shells, as named 

 varieties, many of which have been established as different species by Kayser. Of 

 these G. retrorsus typus, Sandb.,^ most nearly corresponds with our fig. 13, but is 

 evidently distinct from that species as shown by other specimens, not being smooth 

 or elliptic, having more sloping sides and a narrower back, and having the lateral 

 lobes situated much more on the sides of the shell, and more inclined outwards. 

 This form is separated from G, retrorsus, von Buch, by Kayser,^ who unites it with 

 G. simplecV, von Buch, under which head he also groups G. ovatus, Milnst., G, 

 striatulus, Miinst., G. retrorsus lingua, Sandb., G. strangulatus, R^eyserling, and G. 

 retrorsus var. Brilonensis, Kayser. If this synonomy is correct, it only shows more 

 clearly the distinctness of G. psittacinus and of the present species. G. simplex, 

 von Buch,* is a shell with a very open umbilicus and a rapidly increasing spire, 

 though the suture-line is more like that of G. psittacinus than that of the present 

 form. 



HalP figures G. uniangularis, Conrad,^ which looks very like G. retrorsus, but 

 difiers from the present form in the size of its lateral saddles, and the less forward 

 position of its central lobe. 



12. GrONIATITES, sp. PL VI, figs. 15, 15 a. 



Description. — Shell rather small, discoidal, involute, flattened, and centrally 

 depressed. Umbilicus minute, aciculate, deep. Sides of the whorls depressed 

 centrally and then arching in a gently increasing curve to meet in a broadly 

 convex back. Suture-line rising perpendicularly from the umbilicus, bending 

 forward in a shallow saddle to form a small, sharp, lateral lobe, which appears to 

 be followed by a narrow, deep, rather bluntly triangular central saddle, and this 

 by a large, wide, almost semicircular, central lobe. 



Size. — 26 mm. in height and 12 mm. in depth. 



Locality. — A single specimen in the Museum of Practical Greology. 



Remarks. — The specimen described above has given me much trouble, as from 

 its state of fracture the suture -line is very hard to understand. At first I was 

 inclined to unite it with the specimens represented by figs. 13 and 14, but a closer 

 examination has convinced me of its distinctness. Fig. 13 represents a specimen 

 belonging to the same species as figs. 9 — 12, which is more nearly circular than 



1 1851, Sandb., ' Verst. Ehein. Nassau,' p. 100, pis. x, x a, x b. 



2 Ibid., pi. X, figs. 14—16, and pi. xa, figs. 3—6, 10, 11. 



'•'• 1873, Kayser, ' Zeitschr. deutsch. geol. Gesell.,' vol. xxv, p. 620, pi. xix, fig. 6. 



* 1832, von Buch., 'tjber Amm. und Gon.,' p. 42, pi. ii, fig. 8. 



' 1879, Hall, ' Pal. N. T.,' p. 444, pi. Ixxi, fig. 14 ; pi. Ixxii, figs. 6 and 7 ; and pi. Ixxiv, fig. 2. 



« 1842, Conrad, ' Journ. Acad. Nat. Sci. Phil.,' vol. viii, p. 268, pi. xvi, fig. 4. 



