part 2] syrijs goth rins and spjbiferina. 165 



The apical callosity iisually increases with the age of the individual, and in 

 ephebic shells completely envelops the earlier-formed portions of the delthyrial 

 supporting-plates and associated structures. Although few of the Spiriferid 

 shells are entirely without an apical callosity, the structure is especially well 

 developed in certain species. When present, it gives a very characteristic 

 appearance to internal casts of the pedicle-valve (see PI. XIII, fig. 12). 



Transverse plate and syrinx. — The transverse plate is an horizontal septum 

 between the delthyrial supporting-plates, and projecting into the interior of 

 the shell from the anterior end of the apical callosity. It may exist as a 

 simple horizontal lamella, or, as in Syringothyrix, it may bear on its lower 

 surface a split tube or syrinx. (See fig. 1 b, p. 166.) l 



II. Syringothtris Winchell. 

 (a) History of Previous Research. 



The earliest account of a species now referred to Syringolhyris 

 was given by William Martin in 1796, when he described Anomia 

 cuspidata from the 'Limestone' of Castleton (Derbyshire). 3 

 Thirteen years later he again described and figured Cnncliylio- 

 lithus anomites caspidatus in his ' Petrifacta Derbiensia,' 3 but 

 dealt only with the external characters of the shell, there being 

 nothing in his specimen to suggest the existence of internal struc- 

 tures. Martin compared the shell to the recent Anomics, and 

 suggested that the large triangular area was the surface of attach- 

 ment, and that the muscles of fixation passed through the narrow 

 fissure (that is, the delthyrium). 



Although several authors referred to and illustrated this remark- 

 able shell during the following thirty years or so, 4 no additional 

 characters were discovered until 1838, when Gr. P. Deshayes 

 recorded the presence of a convex plate (deltidium) covering the 

 delthyrial fissure. That author stated that the plate was provided 

 near the apex with an oval foramen. 5 



A similar opinion was expressed by Thomas Davidson, who 

 figured an internal cast of ' Sjiirifera cuspidata^ from the 



' dolomitic Carboniferous Limestone of Breedon Hill, in which there is evidence 

 that the deltidium was in reality perforated by a circular foramen.' 



1 The words 'upper' or 'lower,' and 'above' or 'beneath,' iised in connexion 

 with the transverse plate and syrinx, refer to the structures when the shell is 

 held with the apex of the pedicle- valve away from the observer, and the beak of 

 the brachial valve pointing upwards, as in the sections in fig. 1 (p. 166). They 

 have no reference to the position of the shell during the life of the individual. 



2 W. Martin [22] p. 44 & pi. iii, figs. 1-4. 



3 W. Martin [23] pi. xlvi, figs. 3-4 ; pi. xlvii, fig. 5. Martin's type-specimen 

 is now preserved in the Sowerby Collection, in the C4eological Department 

 of the British Museum (Natural History). 



* J. Parkinson [26] vol. iii, pp. 234-35 & pi. xvi, fig. 17 ; J. Sowerby [33] 

 pp. 42-44 & pi. cxx, figs. 1-3 ; J. Fleming, ' A History of British Animals ' 

 (1828) p. 563. 



5 Deshayes in ' Histoire Naturelle des Animaux sans Vertebres ' 2nd ed. 

 vol. vii (1838) p. 368. 



* Davidson |4] explanation of pi. viii, footnote, and pi. ix, figs. 1-2. The 

 specimen is now in the Davidson Collection, in the British Museum (Natural 

 History). 



