6 BRITISH CARBONIFEROUS BRACHIOPODA. 



panied by copious illustrations. The difficulty of discriminating becomes also even more 

 sensible when a genus is largely represented in any single or contiguous group of strata, 

 as are, for example, the Spirifers and Productuses, which in no other epoch were more 

 varied or half so abundant as in the Carboniferous period ; they also here attain their 

 maximum of development both in number of species and proportions, as maybe exemplified 

 by the well-known full-grown individuals of Sp. striata and Pr. giganteus. The compara- 

 tive length of the hinge line, as well as number of ribs, is so variable, not only according 

 to age but from other natural and extraneous causes, that it becomes at times most 

 perplexing to know where to find words sufficiently precise or explicit, so as to convey a 

 clear idea of those minute differences which exist, and which suffice in many cases to 

 warrant the specific or varietal separation of two seemingly allied forms. 



It has been my strenuous endeavour, as far as the space at my command would admit, 

 to figure not merely one marked individual, but likewise others less characteristic 

 in their features ; that the general observer may feel less embarrassed how to deal with 

 the more numerous intermediate variations in shape, so prevalent among the species of this 

 class of Mollusca. 



Among the numerous works and papers which have been consulted during the 

 preparation of the present monograph, I feel bound to call attention to a few British ones 

 in particular, not merely from their importance, but also to satisfy the reader as to the 

 source whence a large portion of our material was derived. 



In the valuable ' History of Rutherglen and East Kilbride,' 1 published by David Ure, 

 in 1793, we find some very passable figures of from eleven to twelve species of Carbonife- 

 rous Brachiopoda, which illustrate in a satisfactory manner a not inconsiderable number of 

 those forms so abundantly distributed in the parishes of Kilbride and Carluke, Scotland ; 

 but the author unfortunately does not apply to them any distinctive specific appellations : 

 he classes his specimens into Anomitee laves, Striata, and Echinata, the last comprising 

 those species with spines, such as Productus. In the 'Mineral Conchology' we find 

 described and illustrated a few more Scottish species, while others are briefly described, 

 but not illustrated, by Dr. Fleming, in his excellent book on 'British Animals,' 1828. In 

 these works, and that of Sowerby, will be found the principal records and illustrations 

 of the Carboniferous Brachiopoda observed in Scotland; but the researches I have 

 undertaken, with the assistance of several kind friends, will enable me to considerably 

 augment the list of the species from that portion of the British Empire, although it has 

 hitherto proved much less prolific than both England and Ireland. 



Some years after Ure's publication, W. Martin's work, 'Petrifacta Derbiensia' (1809), 

 appeared, in which about nineteen species of Brachiopoda were described and carefully 



1 It is now a scarce volume, and not generally known, but is well deserving of an honorable mention, 

 being the first work in which Scotch fossils were correctly described and delineated. Specimens identical 

 with and from the localities of David Ure were both lent and presented to me by several Scottish friends, 

 and will be found illustrated in the present work. 



