380 GENERAL SUMMARY TO 



7. Strophodonta, Hall, 1850. Type Stroph. demissa, Hall. 



8. Tropidoleptus, Hall, 1857. Type Trop. carinatus, Conrad. 



9. Leptana, Dalman, 1828. Type Lept. transversalis, Dalman. 



The question to be hereafter determined is whether all the foregoing genera are distinct, 

 or if the number might not be reduced, especially in what relates to Streptorhynchus, 

 Orthotetes, and Berbyia, which seem to be nearly connected and separable with difficulty. 



The larger number of families and genera, as well as of species, prevailed during the 

 Palaeozoic period. The Terebratulida, however, predominated during the Neozoic time ; 

 and have been both generically and specifically most numerous along with the Bhynchonella 

 in the Jurassic, Cretaceous, and Recent periods. During the Permian and Triassic epochs 

 the Brachiopoda were comparatively poorly represented. Nineteen genera referable to 

 six families are now found alive in our sea-bottoms. 



Experience has taught us that, although some few cosmopolitan species occur in 

 the same formation in districts far separate, it is not the less certain that the faunas 

 referable to the same epoch at a distance, are mainly dissimilar, or show a great proportion 

 of species peculiar and limited to the district in which they occur. The geological range 

 of the larger number of species is therefore comparatively restricted, and numerous 

 examples to this effect could be adduced. 



As stated by Barrande in his admirable memoir ' Epreuves des Theories Paleonto- 

 logiques par la realite ' the Brachiopoda, after the Trilobites, occupy the most important 

 place in the Cambrian or Primordial fauna. Thus in 1871, out of 241 species known to 

 him as composing the animal kingdom of that period, 179 were referable to the Trilobites 

 and other Crustacea, twenty-eight to the Brachiopoda, while thirty-four species 

 were divided between the Annelida, Pteropoda, Gasteropoda, Bryozoa, Cysfidea, and 

 Sponyida. Subsequent to these statements, many additional species of Trilobites and 

 Brachiopods and forms referable to other classes have been added to the list through the 

 indefatigable researches of the late Prof. Linnarsson, Barrande, Dr. Hicks, and some 

 others, but which do not invalidate the general conclusions arrived at by Barrande. 



The Brachiopoda, together with the groups mentioned, are the earliest representatives 

 of life at present known, for Dr. Hicks obtained undoubted examples of Lingulella and 

 Biscina from the very base of the Cambrian series in Wales. Although the Trilobites 

 occupied the most important place in the Lowest Cambrian or primordial fauna, they fall 

 short of their importance to the geologist when taken in comparison with the Brachiopoda, 

 which have continued to be extensively represented from the base of the Lower Cambrian 

 up to the present time, while the Trilobites are restricted to the Palaeozoic period. They are 

 also very characteristic fossils, by which rocks at great distances, whether in New Zealand 

 or Spitzbergen, in the Himalayas or the Andes, can be identified without its being 

 necessary for the palaeontologist to visit the district from whence the fossils were derived. 



It is impossible, in the present state of our knowledge, to offer more than a very 



