President's Address. 



79 



From Orthoceras we pass to Acf/inoceras, in wliicli the shell 

 resembles the former, but the siphuncle is unusually large, 

 inflated between the chambers, and having a slender central 

 tube. Only one species has at present been described in the 

 British Carboniferous series, the Actinoceras gigantev/ni (Sby.), 

 one of the largest of all the Orthoceratidfc. This species is 

 sometimes met with many feet in length, and with a corre- 

 sponding circumference. This is especially the case with 

 specimens from the Closebu'rn Limestone, Dumfriesshire, the 

 locality from which Mr James Sowerby's original specimen 

 was derived. Mr Sowerby estimated the size of his speci- 

 men when complete at exceeding 8 feet.* Another favourite 

 locality for this gigantic fossil, according to Messrs Arm- 

 strong and Young, is Orchard Quarry, where "instructive 

 examples, showing the large-headed siphuncle " are met 

 with. 



In the genus Cyrtoceras (Goldfuss), w^e find simply a curved 

 or horn- shaped Orthoceras with a small siphuncle, generally 

 subcentral to dorsal. Three species are met with in Scot- 

 land, and only about two more are known in the Carboni- 

 ferous Limestone of England. Cyrtoceras rugosum (Fleming, 

 sp.) is perhaps the most characteristic species, and was 

 originally described by Dr Fleming as an Orthoceras. Pro- 

 fessor M'Coy described the genus under the name of Campy- 

 loceras, but his name has to give place to that of Dr 

 Goldfuss. 



Professor de Koninck gives a rather complicated arrange- 

 ment of Cyrtoceras expressed by the following table : -f* 



Group A. — Cyrtocerata Exogastrica — 

 Sec. 1. Lcvvia, siphon cylin<lroid. 

 ,,2. ,, ,, numiiniloid. 



,, 3. Ornata, ,, cylindi-oid. 

 ,,4. ,, ,, nuiiiinuloid. 



Group B. — Cyrtocerata Endogas- 

 trica — 

 Sec. 1. Ornata, siphon cylindroid. 

 ,, 2. Lcevia, ,, nummuloid. 



The last genus of this Family to be noticed is Gomj^hoccras 

 (J. de C. Sby.).j The Carboniferous species placed here are 



* Min. Con., iii., p. 81. 



+ Faiine du Calc. Carbonif. dc la Be]gi(iiie, 1880, pt. 2, p. 17 



t Murchison's Sil. System, 1839, p. G21. 



