PRELIMINARY REMARKS. 5 



Perhaps the fossils of the Cretaceous period have attracted more attention than those of 

 any other system ; a great many valuable works and memoirs are published on the 

 subject by Sowerby, Rcemer, Geinitz, Reuss, Nilsson, Wahlenberg, D'Archiac, Brongniart, 

 &c. ; but the most complete is undeniably that of M. D'Orbigny's, ' On the Species of 

 France,' although we regret not being always able to coincide in the determinations and 

 observations communicated by that distinguished Palaeontologist ; our researches, both in 

 the field and in collections at home and abroad, having led us to different results. 



Notwithstanding that in some cases we may be mistaken, still our exertions have tended, 

 we hope, to correct various errors prevalent, especially on the continent, where some of 

 our British types are singularly misunderstood by authors who have not had the same 

 advantages as ourselves of comparing their specimens with the original types preserved in 

 this country. It may at the same time be remarked that, from the vast number of 

 individuals obligingly forwarded from all quarters, we have succeeded in tracing some 

 passages of form ; and the great confusion in the nomenclature has arisen from describing 

 species on the study of only one or two specimens ; indeed, so perplexing are the minute 

 shades that link certain shapes together, that we have often been embarrassed and uncertain 

 where to draw a line of demarcation. 



The internal arrangements of the calcareous appendages or muscular impressions are 

 similar in all the individuals of the same species, and although diversified to some extent in 

 different forms of the same genus, these last are sufficiently constant to warrant separation. 1 

 Our British Cretaceous period is very rich in species of Brachiopoda, but not so much 

 so as in France, from being deficient in certain beds, which are there very prolific in a 

 variety of forms. I am happy to say that among the numerous British specimens kindly 

 lent to me, I have discovered a number of forms found on the continent, but unknown 

 and unpublished in our English catalogues. 2 



We have admitted twelve genera among our Cretaceous Brachiopoda, viz., Lingula, 

 Crania, Thecidea, Argiope, Magas, Terebratella, Trigonosemus, Terebrirostra, Terebratulina, 

 Kingina, Terebratula, and Bhgnchonella, and will elsewhere discuss their respective value 

 and claims as sections in the class of Brachiopoda ; they are based on important internal 



1 In page 7, Part III, I noticed the absolute necessity of abandoning the use of the terms dorsal and 

 ventral in the descriptions of Brachiopoda, and proposed the use of other denominations. Since the 

 publication of the above, Professor M'Coy, ('Annals and Mag. of Nat. Hist.,' Nov. 1851, vol. viii, p. 391,) 

 following out these views, proposes to make use of tbe terms receiving valve for the imperforated valve of 

 Terebratulce, &c, and entering valve for the opposite one, of which the beak enters into the cavity of the 

 receiving one. I have no objection to the use of these terms in the sense employed by Professor M'Coy, 

 but should have preferred the name dental valve for the perforated one, and socket valve for the other. The 

 use of two or three terms to designate them will be found of great convenience where the same technical 

 designations must be often repeated. 



2 I am particularly obliged to Mr. S. Woodward for lending me a numerous suit of sketches of 

 British Cretaceous Brachiopoda, preserved in various cabinets, which enabled me to procure the loan of the 

 original specimens for illustration and description. 



