1 68 INVERTEBRATE PALAEONTOLOGY 



(probably brackish) horizons in the Coal Measures, 

 while Archanodon from the Old Red Sandstone (doubt- 

 fully placed in this group) is the oldest known fresh- 

 water Pelecypod. Isodonta began to show some pro- 

 gress in Carboniferous times ; both of the common 

 stocks, Pecten and Lima, date from that period. But 

 the most important member of the series is Pterineo- 

 pecten (PL xii. fig. 2), one of the commonest fossils of 

 marine bands in the Lower Coal Measures. Modiolus, 

 a living genus of Dysodonts, appeared in the Devonian, 

 while the rock-boring Lithophagus has been recorded 

 from the Carboniferous. The only Palaeozoic family 

 of Anomalodesmacea (Pholadellidae) is represented by 

 Allorisma,) a mussel-shaped shell not uncommon in the 

 Carboniferous, but rare in the Permian. Records of 

 Teleodesmacea from the Upper Palaeozoic are doubtful, 

 but Pleurophorus, if rightly placed in this order, gave 

 it abundant representation in the Permian. The de- 

 generate, burrowing types of P kolas and Teredo are said 

 to occur in the Carboniferous, but quite different animals 

 might have produced the crypts ascribed to them. 



Aspidobranchiate Streptoneura retained their promi- 

 nence among Upper Palaeozoic Gastropods. Many of 

 the genera that occurred in the Silurian, such as Belle- 

 rophon (PL xii. fig. 4), Murchisonia and Euomphalus, 

 survived into the later era with equal, or greater, 

 numbers. The Euomphalidae are particularly charac- 

 teristic of the Carboniferous Limestone, Euomphalus 

 (PL xii. fig. 3), Schizostoma, Straparollus and Platyschisma 

 being familiar genera. The small, limpet-like Fissurel- 

 lidae made their appearance at that horizon ; Naticopsis 

 was perhaps a precursor of the common Neritidae of 

 to-day. Among Ctenobranchiate types few innovations 

 were made at this stage. Gymnoglossa were still repre- 

 sented by MacrocheiluS) and especially by Loxonema\ 



