56 DEVONIAN FAUNA. 



Phragmoceras ? (1), Gomphoceras ? (2), Poterioceras (3), Orthoceras (15), and 

 Actinoceras (1). Clymeuia is not represented in these beds. 



It is often a matter of difficulty to decide the generic as well as the specific 

 positions of these fossils. On account of the peculiar character of the Limestones, 

 the species being generally of large size, perfect specimens are rare ; and, as the 

 characters frequently change in different parts of the same shell, as well 

 as alter with the age of the specimen and vary in different examples of a 

 similar age, it becomes sometimes very difficult to allocate the fossils to their 

 proper specific place. 



The perplexity becomes in some instances even greater when we try to decide 

 the genus. The oral portion of the shell being unsupported by septal walls is the 

 part most liable to destruction, and the aperture itself is consequently hardly ever 

 preserved. Hence in the case of such genera as Gomphoceras and Poterioceras it 

 is almost impossible to speak with any degree of certainty. 



Order.— TETRABRANCHIATA. 



SuB-oRDER.— AMMONOIDEA. 



I. Family. — Goniatitid^. 



1. Genus. — Goniatites, de Haan, 1825. 



This large genus, which appears to be confined to the Devonian, Carboniferous, 

 and Permian Rocks, has been divided by Beyrich, Sandberger, Hyatt, and others 

 into groups, which are founded upon the shape of the suture-lines. Where possible, 

 therefore, the suture-lines have been given in the accompanying plates, but they 

 have proved very difficult to copy accurately for various reasons, and they have been 

 observed in too few of the species to admit of their being grouped under these 

 divisions in the present work. Those that are known, however, seem to belong 

 to one of Beyrich's three divisions, Nautilini, Simplices, and Primordiales. 



1. Goniatites obliquus, Wlddhornc. PI, V, figs. 1—3. 



1852. Goniatites planidoesatus, Geinitz (not Munster). Verst. Grauw. Sachsen, 



pt. 2, p. 39, pi. xi, figs. 4—6. 

 1889. — OBLIQUUS, Whidh. Geol. Mag., dec. iii. p. 29. 



Description. — Shell large, discoidal, of four or five whorls. Umbilicus wide, 

 shallow, about one quarter the diameter of the shell, scalariform, showing the 



