192 . DR. F. .1. SOUTH ON vol. lxXVl. 



especially those near the fold, show a tendency to bifurcation, a 

 condition not found in any shell in which Syringotlrp-oid characters 

 have been proved to exist. 



The fold is divided by a shallow median depression into two 

 broad, low, rounded costse, and the depression itself may or may 

 not be slightly undulated. The sinus is marked by about eight 

 eostae, quite distinct, but not so well developed as those on the 

 lateral slopes of the shell. 



I have not succeeded in obtaining any evidence of the existence 

 of punctations in the shell-structure ; but, for reasons which 

 have already been given, that does not necessarily prove their 

 absence, since all the specimens were either recrystallized, silicified. 

 or partly exfoliated. 



The elongate type of Spirifer distans is strongly suggestive of 

 the shell described hx M'Coy as Sp. bicarinata, 1 but his single 

 figure inadequately represents it. Subsequently, however, Davidson 

 re-figured the original specimen in another position, and his illus- 

 tration, 2 together with M'Coy's description, leaves little doubt as to 

 the identity of the specimen. As ahead}? - mentioned, the normal 

 and the elongate types are connected by intermediate forms, and 

 there are no grounds for regarding them as distinct species; but the 

 name bicarinata may conveniently be used as a varietal name to 

 designate specimens of the latter type. The significance of the 

 two names would then be as follows : — 



(1) Sp. distans Sowerby (text-fig. 3 a, p. 178). 



Shell ovoid, about or rather less than twice as long as wide ; cardinal 

 extremities rounded. Example: Sowerby, 'Mineral Conchology" 

 pi. ccccxciv, fig. 3 ; and Davidson [4] pi. viii, figs. 1-4. 



(2) Sp. distans, var. bicarinata M'Coy (text-fig. 3b, p. 178). 



Shell distinctly elongated ; greatest diameter at the hinge-line ; more 

 than twice as long as wide ; cardinal extremities angular and pro- 

 duced. In the specimen figured by M'Coy the fold in the brachial 

 valve is slightly concave, but this is only one aspect of the irregu- 

 larly-plicated fold of the species, and has no taxonomic value. 



Example : M'Coy [20] p. 129 & pi. xxii, fig. 10 ; Davidson [4] pi. viii. 

 figs. 11-14, 16 & 18, pi. hi, fig. 5. 



There does not appear to be an}'' record of the occurrence of a 

 transverse plate and syrinx in a correctly-determined specimen of 

 Sp. distans, and in the specimens which 'have been rubbed down in 

 the course of this investigation no trace of any such structure has 

 been observed, although the delthyrial supporting-plates were 

 perfectly preserved. This seems sufficient reason for asserting 

 that no syrinx-bearing plate occurs, and, therefore, that the species 

 does not belong to Syringothyris, but must be referred to Spirifer. 



De Koninck's discovery of the syrinx has already been men- 

 tioned, and it has been shown that the structure which he 

 described was exactly like that of Syringothyris ; it now remains 



1 M'Coy [20] p. 129 & pi. xxii, fig. 10 ; see also Davidson [4] pi. viii. 

 fig. 18, where M'Coy's figure is reproduced. 



2 Davidson, op. cit. p. 224 & pi. lii, fig. 5. 



