part 2] ISYMNGOTHYMS AND SPIRIFEMNA. 221 



imperfect nature and state of preservation, the affinities of the 

 specimen cannot with certainty be determined. The locality of the 

 figured specimen is given as Kildress (Tyrone). 



2. A specimen described as ' near to ' octoplicata, but having more costas 

 than that form 1 : in this case, however, the specimen does not appear 

 to have been preserved. 



Additional Note upon Spir'iferina. 



It is, perhaps, scarcely necessary to mention that, although the 

 three Carboniferous species of Spiriferina enumerated can be readily 

 recognized even in their early mutations, as well as in their mature 

 condition, there are no hard-and-fast lines of distinction between 

 them. Regarded as a whole and as members of a genus, they are 

 sharply differentiated from contemporary forms, and are an 

 interesting example of evolution in a ' sheaf of parallel forms.' 3 



The young stage (in a phylogenetic sense), with small and simple 

 forms, occurs in the Lower Avonian, and the adult stage, in which 

 the full size was reached and the essential characters fully developed, 

 was attained in Dibunophyllum times. 



There are other forms which represent species additional to those 

 enumerated here, but they are less common, and a discussion of 

 their characters is reserved for a future paper. 



VII. Summary of Conclusions. 



1. The special characters of Syringoihyris were first described 

 by L. Gr. de Koninck in a Belgian specimen wrongly identified as 1 

 Spirifer distans. The name Syringoihyris was proposed by 

 A. Winchell, who discovered in a North American Carboniferous 

 shell, characters similar to those already noticed by De Koninck. 

 The existence of the syrinx in 8. cuspidata (Martin) was first 

 recorded by F. B. Meek. 



2. The essential characters of the genus are : — its strongly cuspi- 

 date outline, a fold and sinus devoid of plications, an imperforate 

 deltidium, a finely and sparsely punctate shell-substance, and a 

 syrinx-bearing transverse plate between the delthyrial supporting- 

 plates. 



3. The satisfactory classification of the forms included in the 

 genus is a matter of some difficulty, owing to the nature of the 

 variations which occur. Variations due to time, to environmental 

 conditions, and to distribution in space are recognized ; and dis- 

 tinctive names are given to the mutations characteristic of certain 

 horizons. 



4. The syrinx and the transverse plate to which it was attached 

 originated as a modification of an apical callosity such as existed 

 in many Spiriferoid shells. It was initiated in Middle Devonian 



1 J. Portlock, ibid., pi. xxxviii, fig. 8. 

 " 3 See, for example, Vaughan [35] p. 3. 



