68 BRITISH OOLITIC AND LIASIC BRACHIOPODA. 



other divisions up to the Portland Oolite, or uppermost member of the series, the number 

 of species diminish, and in some beds, only one or two forms have yet been noticed ; 

 thus in the Kimmeridge Clay, I am only acquainted with two, B. inconstans and 

 B. subvariabilis; in the Portland beds, none seem as yet to have been discovered. 

 Certain forms are rare, others very common. Among the former, I may mention 

 B. Wrightii, furcillata, subvariabilis, ringens, serrata, and among the latter, B. con- 

 cinna, obsoleta, acuta, varians, variabilis, inconstans, spinosa, and tetraedra ; if, again, 

 we glance over our table to see what takes place among the other genera, especially the 

 Terebratulce, we observe a similar poverty of species and individuals in the upper portions 

 of the Oolitic system. There existed, therefore, at that period, a sea, and circumstances 

 more favorable to the development of this class of Mollusca, which after diminishing 

 appeared again in the Cretaceous epoch in vast numbers. I may conclude these few 

 remarks by stating, that from the extreme variability of shape in this most difficult genus, 

 it is at times scarcely possible to compare specimens with figures ; and the more so when 

 the latter are unexact or executed so carelessly as to place one in great doubt as to the types 

 intended ; this is proved by the multitude of erroneous determinations or synonyms filling 

 most Geological and Palaeontological works ; the mistaken identification of species attributed 

 to Sowerby and Lamarck, would alone fill the space of several sheets, nor should I have been 

 able to determine many of the shells which have come under my notice, had I not been 

 assisted in my comparisons by the original specimens of the 'Min. Con.,' and those of 

 Lamarck, &c. 



examples of his genus Rhynchonella, while not one of the types of Trigonellce can be safely identified, 

 excepting the last, which is a true and well-known Spirifer ; it appears, likewise, that in 1778, Da Costa 

 proposed a genus Trigonella for a Mactra, and De Candolle the same for a section of Plants. 



Davila, in 1767 {'Catalogue Systematique et Raisonne" des Curiosites de la Nature,') gives a few 

 good illustrations of some recent Terebratulse, and shows, by his various observations, that he had not 

 neglected to remark the differences of the internal apophysary system between the true Terebratulce and 

 Rhynchonellce while describing his Bee de Perroquet, the name by which R. psittaeea was then well known ; 

 he alludes to the hinge, and the two short lamella. 



In 1712, Morton {'Nat. Hist, of Northamptonshire,'') perceived the necessity of separating the plaited 

 Terebratulee from the smooth ones. He adds, p. 211, "The head or beak of the longer of which valves 

 is crooked, and lies over the top of the other valve : of these, there are two general divisions, the smooth 

 and the striated; the smooth have generally a rounder and blunter beak, the end of which in most of them 

 is, as it were, bored, from whence it was called Terebratula by Lhwyd, in his ' Lithop. Brit.' Some have 



a rounded, others a straight margin in the second division, the striated ones have generally a 



sharper beak than the former;" this shows, that so far back as 1712, the necessity of separating the 

 Rhynchonellce from the true Terebratulse was appreciated. 



For further details, refer to ' Introduction,' and the article ' Rhynchonella,' in Parts I and II, where 

 numerous illustrative figures are given, and to my paper in the 'Ann. and Mag. of Nat. Hist.,' April 1852. 



