2 DE. T. DAVIDSON ON EECENT BEACHIOPODA. 



him up to that date. In this catalogue without figures, ahout one hundred species are 

 enumerated, some of which are synonymous. 



During the last thirty-five or more years, I have devoted much time to the study of 

 the recent forms, in conjunction with that of the fossil species, and have lost no oppor- 

 tunity of making myself acquainted with all that has been done and written upon the 

 subject, as well as in assembling all available material, so as to enable me to bring 

 together in a single monograph the chief results of many independent researches published 

 in a number of scattered papers and works often difiicult of access. The literature of 

 the subject is indeed voluminous, as may be realized by a glance at the ' Bibliography 

 of the Brachiopoda,' compiled by Mr. W. H. Dalton and myself, and published in vol. vi. 

 of my ' British Fossil Brachiopoda ' (Palfeont. Soc, 1886). 



I have also, I believe, had advantages which few have possessed in being able to follow- 

 out the observations made with respect to the animal and its anatomy, and in having 

 been able to draw a very large number of figures from the types of the best-preserved 

 examples of almost all the known forms, as well as of a large series of individuals of 

 the same species at different stages of development. Tlie study of the adult condition of 

 a species gives insufficient data, and it is requisite to follow out the modifications it has 

 to go through during the different stages of its existence, and to note these differences. 



The study of the embryo has also shown that the animal assumes a series of well- 

 defined stages in its development, a fact that was but little known prior to the publi- 

 cation in 1861 of Prof. Lacaze-Duthiers's admirable memoir on Thecidium medi- 

 terraneum. These observations were subsequently followed by the excellent 

 researches of Fritz Muller, Kowalcvsky, E. Morse, II. Friele, M'^Crady, Dall, Van 

 Bemmelen, A. E. Shipley, M. A. Schulgin, and one or two more. The results 

 obtained by these authors will be referred to in the sequel. It is very desirable that 

 these important investigations should be continued, as much still remains to be 

 discovered, described, and illustrated. 



The shell-structure of the recent Brachioiioda has been admirably worked out by a 

 number of accurate observers, such as Dr. W. B. Carpenter, W. King, Van Bemmelen, 

 Hancock, and many others, and has led to very important results. To Herman Friele, 

 E. Deslongcbamps, and one or two others we are indebted for much accurate and im- 

 portant knowledge with respect to the development of the loop, of which but little was 

 known previous to 1852. 



The anatomy of the animal has also l)een admirably investigated and worked out, and 

 it is sufficient to mention the names of Cuvier, Owen, Huxley, Hancock, Vogt, Gratiolet, 

 Lacaze-Duthiers, King, Brooks, Dall, Morse, E. Deslongcbamps, Van Bemmelen, Wood- 

 ward, Shipley, Schulgin *, and others, to show how important and varied have 

 been the additions to our knowledge with respect to this very necessary branch of 

 investigation. In drawing up the description of each species, I have considered it 

 desirable, whenever possible, to reproduce the words and illustrations of the authors, and 

 thus give them all credit for their careful, painstaking researches. 



* To these names Dr. Davidson would doubtless have added that of H. G. Be3-er, who contributed an important 

 paper on the shell-structure and anatomy of Lmr/ida {Glottidia) pyramidata, Stimpson, to the Studies from the 

 Biological Laboratory of the Johns Hopkins University, Baltimore, vol. iii. no. 5, March 188(3. — [xi. C] 



