436 Rev. W. A. Leigliton on the British Graphidese. 



O. ornatus, Egerton. Under the designation of specific cha- 

 racters may be noticed the delicate striated surface ornament of 

 the head bones of this fish, and the highly ornamental pattern 

 on the scales. 



Locality. Lias, Lyme Regis. Decade 8. pi. 9. 



Genus Pycnodus, Agass. 



P. liassicus, Egerton. This, the only specimen of the genus 

 found so low as the Lias, is remarkable for the tuberculate orna- 

 ment on the scales, and the variety in the size and form of the 

 teeth. 



Locality. Lias, Barrow on iSoar. Decade 8. pi. 10. 



Plates illustrative of the above species, beautifully drawn and 

 lithographed by Mr. Dinkel, may be seen at the Meeting of the 

 Geological Society on the 7th of June. 



I have the honour to be. Gentlemen, 

 Your obedient servant, 



P. DE M. Grey Egerton. 

 6 Albemarle Street, May 15, 1854. 



XL. — Monograph of the British Graphidese. 

 By the Rev. W. A. Leighton, B.A., F.B.S.E. 



[Concluded from p. 395.] 

 8. Arthonia, Ach. 



Apothecium (ardella) roundish, or difformed, tumid, innately 

 sessile, covered with a subcartilaginous membrane, within sub- 

 gelatinous, containing immediately under the surface a series of 

 pyriform asci ; perithecium none ; disk nearly plane, not bor- 

 dered, black, rough. Thallus cartilagineo-membranaceous. 



" Name from dp6(o to sprinkle, according to Acharius, because 

 the numerous apothecia are as it were sprinkled over the crust : 

 but M. Fee justly remarks that dpSco (and not dpOo)) is to sprinkle, 

 and that therefore the name ought to be Ardonia." Hook. Br. 

 n. 2. 142. 



I propose to designate the apothecium by the term ardella, 

 significant of its appearance as a sprinkled spot. 



1. Arthonia epipasta, 13. microscopica. Thallus thin, mem- 

 branous, smooth, shining, grey or copper-coloured, irregularly 

 circumscribed; ardellse innate, scattered, oblong or elongate- 



