1 86 



HISTORICAL PALEONTOLOGY. 



and South America; whilst P. longispina (fig. 127, b) has a 

 distribution little if at all less wide. 



The higher Mollusca are abundantly represented in the 

 Carboniferous rocks by Bivalves (Lamellibranchs), Univalves 

 (Gasteropoda), Winged - snails (Pteropoda), and Cephalopods. 

 Amongst the Bivalves we may note the great abundance of 

 Scallops (Aviculopecten and other allied forms), together with 

 numerous other types some of ancient origin, others repre- 

 sented here for the first time. Amongst the Gasteropods, we 

 find the characteristically Palaeozoic genera Macrocheilus and 

 Loxonema, the almost exclusively Palaeozoic Euomphalus, and 

 the persistent genus Pleurotomaria ; whilst the free-swimming 

 Univalves (Heteropodd) are represented by Bellerophon an&Porcel- 

 lia, and the Pteropoda by the old genus Comdaria. With regard 

 to the Carboniferous Univalves, it is also of interest to note here 

 the first appearance of true air-breathing or terrestrial Molluscs, 

 as discovered by Dawson and Bradley in the Coal-measures of 

 Nova Scotia and Illinois. Some of these ( Conul'us priscus) are 

 true Land-snails, resembling the existing Zottites ;. whilst others 

 (Pupa vetusta,^. 128) appear to be generically inseparable 

 from the " Chrysalis-shells " 

 (Pupa) of the present day. 

 All the known forms three 

 in number are of small size., 

 and appear to have been local 

 in their distribution or in their 

 preservation. More import- 

 ant, however, than any of the 

 preceding, are the Cephalo- 

 poda, represented, as before, 

 exclusively by the chambered 

 shells of the Tetrabranchiates. 

 The older and simpler type of 

 these, with simple plain septa, 

 and mostly a central siphuncle, 

 is represented by the straight 

 conical shells of the ancient 

 genus Orthoceras, and the bow- 

 shaped shells of the equally 

 ancient Cyrtoceras some of 

 the former attaining a great size. 

 The spirally-curved discoidal 

 shells of the persistent genus Naictilus are also not unknown, 

 and some of these likewise exhibit very considerable dimen- 

 sions. Lastly, the more complex family of the Ammonitidce, 



i (D;ndropnpa)vetnsta. 

 aii fr 



Fig. ii 



a Carboniferous La.id-snaii from the Coal 

 measures of Nova Scotia, a, The shell, of 

 the natural siza ; b, The same, magnified ; 

 c, Apex of the shell, enlarged ; d, Portion 

 of the surface, enlarged. (After Dawson.) 



