164 THE TRANSFORMATIONS OF THE ANIMAL WORLD 



the Pectinidse comprises Chlamydes from the 

 Triassic period, and Amussia from the Lias ; the 

 marine mussels or Mytili have changed little 

 since the Trias. The Gastropods also show a 

 few branches with very tenacious forms ; the pate- 

 lo'id shells of the genus Acmcea have existed with 

 hardly any modification since the Cambrian ; the 

 rare Pleurotomaria of the present day is connected 

 with a series of very abundant forms in the Ju- 

 rassic ; the Fissurellae, the Pseudomelanice have been 

 known since the Carboniferous ; the Capulus is 

 present in the whole series of fossiliferous strata ; 

 the existing Actceonina commences with the Car- 

 boniferous ; the terrestrial Pulmonates of the Pupa 

 group have been discovered as early as the Coal. 

 The bivalve carapaces of the Phyllopod Crustacea 

 of the type Estheria abound in the brackish de- 

 posits of all epochs, from the Devonian to the 

 Quaternary ; that of the Ostracods of the living 

 genera, Bairdia, Cytherella, and Cypridina, go 

 back as far as the Ordovician. The Balana of the 

 genus Creusia have fixed themselves to rocks ever 

 since the lower Devonian. The present Limuli 

 have for precursor a small species discovered in 

 the lower Trias of the Vosges. The Eoscorpius of 

 the Carboniferous strata of Illinois and the Protoly- 

 cosa of the Coal of Silesia differ but little from our 

 present scorpions and our existing spider Lycosa. 



As a set off, other phyletic branches have had a 

 more rapid evolution. I have already referred 

 to the curious example of the Levantine Viviparas 

 which, during the Pliocene epoch alone, passed 

 from their first smooth form to carinated and 



