﻿Vol.64.] HOMOEOMOKPHY : '' SPIRIFER GLABEB.^ 31 



distinguished from Brackythyris by being broader and flatter. No 

 dental plates.^ 



British species : — /Sp. eximius, de Kon. ; ' Sp. subrotundatus ' ; 

 Anomites cjlaher. 



Genus Eetictjlaeia., M'Coy. 



(Type : Eeticularia reticulata, M'Coy) 



Spiriferids with reticulate surface — the final forms become nearly 

 or quite smooth. Distinct dental plates. 



British species : — Sp. imbricatus ; Reticularia reticulata ; Anomites 

 lineatus ; Sp. mesoloba ; Martinia stringocephaloides ; Sp. elliptica,^ 

 Phill. ; Sjy. glaberrimus, de Kon. in Dav. ; Sp. glaber, auctt. = ?/Sp. 

 latits. Brown ; Sp. glaber, Phill.^ non Martin. 



The various species of smooth Spirifers mentioned at the beginning 

 of this article as being grouped under the name Sp. glaber have 

 now been distributed into three genetic series. There are two 

 exceptions, Sp. symmetrica and Sp. decora. The first, which differs 

 from Sp. oblatus in deficiency of mesial fold, may perhaps be 

 assigned to Brackythyris ; but Sp. decora does not appear to fit in 

 anywhere. The types of these two species do not seem to possess 

 any dental plates. 



Note. — Some, perhaps all, of the British Silurian species of Spirifer would 

 be correctly classed under the genus Delthyris, Dalman. 



Appendix. 



Kevised Explanations of Davidson's pis. xi & xii^ ' Monogr. 

 Carb. Brach.' (Palseont. Soc.).^ 



Plate 



Fig. 1. Martinia sp. 



2. Martinia glabra, Martin sp. 



3. Eeticularia glaherrima, de Ko- 



ninck sp. Type. 



4. Eeticularia glaherrima, young 



form. 



5. Brackythyris sp., cf. pi. xii, 



fig. 9. 



Fig. 6. Brackythyris symmetrica,'£]\\\- 



lips sp. 

 7. Martinia glabra, Martin sp. 

 Figs. 8, 9. Brackythyris ohlata, Sow- 



erby sp. 

 Fig. 10. Eeticularia mesoloba, Phillips 



sp. 



1 Absence of dental plates is said to be a distinction of Martinia, that is, the 

 ^^aSer-series ; and this character does apply to mai)y smooth forms. But 

 forms with and without dental plates have been called ' Spirifer glaber.'' It is 

 part of the object of this paper to call attention to the necessity of examining 

 all these smooth forms, especially casts, to see which have and which have not 

 these plates. 



So with the costate forms, where dental plates are given as a generic 

 character: it has not been possible to verify their presence or size in regard to 

 all the species attributed to such a genus ; and figures too often fail to give the 

 information. 



^ The type (British Museum, Natural History, B 266) shows in the broken 

 beak strong dental plates. 



^ 'Geol. Yorks.' pt. ii (1836) p. 219 & pi. x, fig. 10. The original specimen 

 shows dental plates. 



'* Subject to what may be discovered by handling the original specimens, 

 now dispersed in niany collections. 



