298 GENERAL SUMMARY TO 



Cyrtina, Nucleospira, Merista, Wliitfieldia, Dayia, Unciles, Athyris, Glassia, Kaysaria, 

 Bifida, Zyyospira, Retzia, Atrypa, &c, all of which have been fully described and illus- 

 trated in the pages and plates of this Monograph. In the RhyncJionellida, again, the 

 apophysis assumes the shape of two short, slender, curved lamellse. Some show large 

 septa and converging plates, as in Pentamerus ; while in many genera and even families, 

 such as in the Orthidida, Strop/io?nenida, Productidm, &c, there exist no calcified 

 supports for the labial appendages. That the animal was possessed of fleshy, coiled, 

 labial appendages is amply proved, for in several species, such as Strojjhomena 

 rhomboidalis, S. Jukesii, and others, the interiors of the ventral valves exhibit in a 

 beautiful and unmistakable manner the impressions of the coils of the fleshy labial 

 processes that were in life affixed to the dorsal valve or to some of the soft parts of the 

 animal. 



At the period I commenced my Monograph, thirty-four years ago, our knowledge in 

 connection with the internal details above very briefly noticed was exceedingly scanty, 

 incomplete, and often unsatisfactory ; and to obtain our present information has neces- 

 sitated long, persevering, and patient research, in which I have been aided by several 

 palaeontologists whose skill and acumen cannot be too loudly commended. 



It would not be possible in this brief summary to allude, in detail, to what each 

 observer had done since 1606 towards the advancement of our knowledge, but in order 

 to make up, as far as possible, for this omission, there has been added a " Brachiopod 

 Bibliography," in which references are given to the majority of such works and papers, 

 and which carries the literature of the subject up to the present time. Towards this 

 compilation several friends have contributed their valuable assistance. Omissions, which 

 we regret, are unavoidable. 



Development of the Loop. — Previous to 1852 we knew very little with respect to the 

 development of the loop in the Terebratulida. In 1853 Dr. S. P. Woodward and myself had 

 observed that a modification in the shape of the loop in the genus Terebratulina took place 

 from the fry to the adult ; for we showed that when it was quite young and up to a certain 

 age the loop was short and simple, as in Terebratula, but that with age it was rendered 

 annular by the gradual union of the oral processes. In very young stages, says Morse, 

 the loop is not yet formed, but the future position of the calcareous loop or crura is indi- 

 cated by a row of irregular-shaped spicula. In the 'Geologist,' vol. iii, p. 144, 1860, 

 Mr. C. Moore published some observations " On the Development of the Loop in Tere- 

 bratella" having previously submitted for my inspection, opinion, and illustration, 

 several very young examples of a small species of Terebratella {T. Buckmani) he had 

 discovered in the Great Oolite at Hampton Cliff near Bath. I made enlarged 

 drawings which were subsequently badly reproduced in pi. xiii of that periodical. Our 

 observations showed that a certain modification in the loop took place prior to its having 

 attained its final full-grown condition. This I likewise subsequently observed to be the 

 case in several other recent and fossil species. The subject, however, in 1875, was 



