I. (Typo specimen.) II. 



7 - 5 mm. 





. 23-5 „ 





• 8-0 „ 





. 15-5 „ 





. 10-0 „ 



8-0 mm 



. 10-0 „ 



8-0 „ 



2G TRlLOBITES OF GIRVAN. 



Dimensions. — 



Length of head 

 Width of „ 

 Length of thorax . 

 Width of „ at front end 

 Length of pygidium 

 Width of „ at front end 



Remarks. — The foregoing description is based on that given by Nicholson and 

 Etheridge, but a few more details have been added after an examination of the 

 types and of other specimens. 



The specimen figured by Nicholson and Etheridge as Dionide, sp., which con- 

 sists of a thorax and pygidinm (supra, No. II), may without much hesitation be 

 also referred to this species, D. lapworthi. Fragments of hypostomes probably 

 belonging to it are also recognisable amongst the Whitehouse specimens. 



Affinities. — Nicholson and Etheridge remark that this species is allied to 

 T). euglypta , Angelin, 1 more closely than to D.formosri, Barrande, 2 and the pygidinm 

 also resembles that of D. atra, Salter, 3 which is the only known part of that 

 species. It, however, appears distinct from all, though the crushed and flattened 

 condition of the type renders this rather uncertain. I am of opinion that its 

 closest affinity is with D. formosa, the long genal spines, the radiating lines on the 

 cheeks, and the pitting of their surface and of the pleuras being in favour of this 

 view, in spite of the greater breadth of the thoracic axis and narrower pygidinm. 



Collections. — Mrs. Gray (f. M.) ; Museum of Practical Geology ; Edinburgh 

 Museum. 



Horizon and Locality. — Whitehouse Group (M. Bala) : Whitehouse Bay. 



2. Dionide richardsoni, sp. nov. Plate IV, figs. 3 — 8. 



1878. Phacops truncato-caudatus, Nicholson and Etheridge, Mon. Silur. Foss. Girvan, fasc. i, p. 99, 



pi. vii, figs. 3, 4. 

 1880. Dionide, sp. ind. («), Nicholson and Etheridge, ibid., fasc. iii, p. 293, pi. xx, fig. 2. 

 Dionide, sp. ind. (d), Nicholson and Etheridge, ibid., p. 295, pi. xx, fig. 5. 



Specific Characters. — General shape oval, expanded in front. Head, thorax and 

 pygidinm of nearly equal length. 



Head semicircular, surrounded by narrow border. Genal angles produced into 



1 Angelin, 'Pal. Scand.,' p. 12, pi. ix, fig. 6 (Polytomurus euglyptus). 



2 Barrande, ' Syst. Sil. Bohe.nie,' vol. i, p. 641, pi. xlii, figs. 24—28. 



3 Salter, ' Mem. Geol. Surv.,' vol. iii, p. 321, pi. xi a, figs. 9, 9 a. 



