lxxxvi TKOCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 1 89 5, 



nuchal furrow, some also with vascular muscle-spot and ocular 

 tubercle. These features evidently have reference to structural 

 modifications of considerable biological value. Leper ditia kept them 

 until the period of the Great Carboniferous Ocean (Mountain Lime- 

 stone) ; but in the subsequent lagoons of the Coal Measures this 

 genus lost its best characters and died out. 



' Primitia, another simple form, contemporaneous with the first 

 mentioned, had the nuchal (dorsal) furrow for its chief character ; 

 but this was soon masked by the swollen edges of the sulcus, 

 indicative of an approach to the form of the Silurian Bollia and 

 Beyrichia ; the latter died out in the Carboniferous period. 



' Of these three types, there are very numerous modifications, 

 varying from the simply undulate surface of the first to the multi- 

 lobed BeyricJiice and intricately-sculptured Octonaria and Strepnda. 

 What the biological significance of the several lobes and lobules may- 

 be is not clear, especially of the hypertrophied antero-ventral lobe of 

 some of the Beyrichice. 



'From Primitia, with its dorsal notch, we may also derive 

 Entomis, with its deep transverse sulcus, and other forms in which 

 this feature dwindles to a subcentral pit, as in KirTcbya and Bary- 

 chilina. In some of these the carapace becomes much ornamented. 

 Some have a strong reticulation, and some a linear or curved striation. 

 These sculpturings pass from one to the other by means of cross- 

 lines, between the longitudinal costulae, forming meshes. KirTcbya 

 ranges from the Lower Silurian to the Permian, where it ceases ; 

 Baryeliilina has been found in the Lower Silurian and Devonian. 



' None of the older genera exist now ; but some of the existing 

 forms of the Cyprididaa, Cytheridse, and Cytherellidse are fully repre- 

 sented by predecessors in the Palaeozoic rocks. The wonderfully 

 well-preserved Palaiocypris Edwardsii (C. Brongniart), enclosed in 

 transparent silica, displaying the soft parts of the animal as perfect 

 as in life, from the Coal Measures of St. Etienne, is evidence of the 

 existence of Cyprids in that far-off time. Carbonia may possibly be 

 a near ally ; at all events there are Macrocypris and other members 

 of the group, including the almost ubiquitous Bairdia, the former 

 ranging from the Lower Silurian to the present day, and the latter 

 from the Devonian upwards. Near the last-mentioned genus are 

 Ulrich's BeecJierella and Krausella, both of Palaeozoic age only. 



' Many diverse forms related to Cypridina flourish at present in 

 the warm seas of different regions, near the surface-waters. Judging 



