496 The Rev. Norman Glass — On Athi/ris Iceviuscula. 



exhibited no trace of this extension of the accessory lamellae. 

 Besides, it was evidently impossible to decide with any certainty 

 that this species was an Athyris whilst the loop and its attachments 

 to the primary lamella were undiscovered. 



Davidson in his Sil. Mon. described three species of Athyris, 

 namely Athyris obovata, A. compressa, and A. depressa — the latter 

 marked by a sign of interrogation. Through his further study, 

 however, and through my own researches, he afterwai'ds in his Sil. 

 Suppl. withdrew the whole of these from the generic denomination, 

 of Athyris. Athyris obovata and A. compressa he determined as 

 being nothing more than modifications in shape of a single species 

 referable to his new genus of Glassia, and in his Sil. Suppl. p. 155, 

 he made the following statement as to Athyris depressa : — " The 

 Eev. N. Glass was able to develop the interior, and to clear away 

 all uncertainty as to the generic position of the shell, for it has the 

 two short, curved lamellae of the genus Rhynchonella." As there- 

 fore the only known representative left of the genus Athyris in the 

 British Silurian rocks, according to Davidson in his Sil. Suppl., was 

 Athyris Iceviuscula, and as I had many doubts at to its real generic 

 position, I determined to avail myself of every opportunity for 

 further investigation. And now, after the lapse of nearly ten years, 

 and after many unsuccessful eiforts to procure suitable specimens, 

 I have at last been enabled fully and decisively to reveal the loop of 

 this species, and thereby conclusively to prove that it cannot possibly 

 be regarded as belonging to the genus Athyris. 



I have to express my thanks to G. H. Maw, Esq., Benthall Works, 

 Jackfield, Shropshire, for his great kindness in sending to me about 

 one cwt. of blunged material from the exposure of the Tickwood 

 beds, by the side of a small stream flowing down the east end of 

 Benthal Edge, opposite Ironbridge. This material I found on further 

 washing to consist of thousands of small pieces of hard rock, 

 innumerable fragments of Corals and Encrinites, many small 

 specimens of Spirifera, Rhynchonella, Nucleospira, etc., and above 

 all a goodly number of the species for which 1 had been so long 

 in search. 



The following descriptions of the loop of Athyris Iceviiiscnla, and 

 of the median septum in the dorsal valve which has hitherto been 

 undiscovered, are based upon a number of my preparations, some of 

 them very minute, and others from four to five lines in length. 



The loop of Athyris Iceviuscula commences from 



the dorsal side of the sj)irals slightly above their 



centre, and consists of two short converging 



lamellae, which arise from the primary lamellae, 



and which proceed in an upward and sloping 



direction between the spirals and right across to 



Ventral aspect of the their ventral side before uniting in a sharp point 



loop of Athijris beneath the hook-shaped attachments to the hinge- 



l(sviuscula, Sow., sp. plate. Arising from this uniting point of the loop 



there is a bifurcation — the two accessory lamellas 



thus formed curving in an upvsiard and backward direction to the 



