ACTINOCERAS. 119 



similar in many respects to the species last described. They cannot be easily com- 

 pared, however, as the upper part of the present fossil is very defective, while in 

 the former shells it is the septal part that is obscure. There seems to be a greater 

 amount of obliquity in the present shell, and it also appears less elongate. I should, 

 however, have united it with the former species but for the great apparent differ- 

 ence in the depth of the septa. As far as can be judged, their depth is twice as 

 great in the present shell as it is in the last at a point where the sectional lengths 

 are nearly the same. Therefore, taking into consideration the two other diver- 

 gences mentioned above, there remains nothing but to regard it as distinct, and 

 there is no other Devonshire species to which it approximates. 



Afl7iities. — 0. subfusiforme, d'Arch. and de Vern.^ (not Miinster), seems very 

 like this shell, but differs in several respects. The sides of its septal parts are 

 quite straight, its section is circular and its chambers are very much shallower. 

 Gomplioceras compressum, F. A. E-omer," is much more elongate, and has closer 

 septa ; and G. ficus, F. A. Romer,^ is more ovoid and elongate, and is marked with 

 strongly raised rings. 



VI. Family. — Actinocbeatidj:. 

 1. Genus. — Actinoceeas, Bronn, 1837. 



The chief characteristic of this genus is the large siphuncle, which is deeply 

 beaded between the septa and contains a syphon of a very compHcated structure. 

 The septa are generally extremely close. It extends from the Cambrian to the 

 Carboniferous. There is no very certain example of the genus occurring in the 

 group of localities which we are now considering; but the specimens described 

 below most probably belong to it. A shell in the Museum of Practical Geology 

 shows that it undoubtedly occurs in the Devonian Rocks of Britain. 0. Ludense, 

 Phillips (not Sowerby), from South Petherwin and Lower Dunscombe, is placed 

 in this genus by M'Coy and Foord. 



1 1842, D'Arch. and de Vern., ' Geol. Trans.,' ser. 2, vol. vi, pt. 2, p. 34.7, pi. xxviii, figs. 2, 2 a. 



2 1850, F. A. Eomer, ' Beitr.,' pt. 1, p. 4, pi. i, fig. 7. 



3 Ibid., p. 38, pi. vi, figs. 1 a, b. 



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