28 TRILOBITES OF GIRVAN. 



is accordingly suggested in honour of the Rev. Peter Richardson, of Dailly, who 

 collected several of the specimens figured by Nicholson and Etheridge in their 

 Monograph. 



It may here be remarked that the two nervures or vascular trunks on the 

 cheeks of Dionide are probably homologous with those mentioned by Gronwall 1 in 

 Gtenocephalus laticeps, Angelin, and Gt. tumidus, Gronwall. Perhaps the structures 

 of similar appearance mAmpyx homeland Salteria prlmseva are of the same nature ; 

 and Jaekel 2 has expressed the opinion that two vascular trunks are characteristic 

 of all Trilobites. 



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

 Museum. 



Horizons and Localities. — Whitehouse Group (M. Bala) : Whitehouse Bay. 

 Drummuck Group (U. Bala) : Thraive Glen ; Drummuck. 



Family Olenid^e. 

 Genus TRIARTHRUS, Green. 

 1. Triarthrus becki (Green), 1832, var. Plate IV, fig. 10. 



1832. Brongniartia carcinodea, Eaton, Amer. Journ. Sci., ser. i, vol. xxii, p. 166 (March). 



Brongniartia carcinodea, Eatou, G-eol. Text-book, p. 33, pi. i, fig. 3. 



Triarthrus beckii, Green, Monthly Amer. Journ. G-eol., vol. i, p. 560, pi. i, fig. 3 (June). 



Triarthrus beckii, Green, Mon. Trilob. N.A., p. 86, cast 34, pi. i, fig. 3. 

 1835. Triarthrus beckii, Harlan, Trans. Geol. Soc. Penn., vol. i, p. 205, pi. xv, fig. 6. 



Paradoxides triarthrus, Harlan, ibid., p. 264, pi. xv, fig. 5. 



Paradoxides arcuatvs, Harlan, ibid., p. 265, pi. xv, figs. 1 — 3. 



Triarthrus beckii, Harlan, Med. Phys. Eesearches, p. 400, pi. xv, fig. 6. 



Paradoxides triarthrus, Harlan, ibid., p. 401, pi. xv, fig. 5. 



Paradoxides arcuatus, Harlan, ibid., p. 402, pi. xv, figs. 1 — 3. 

 1838. Paradoxides beckii, Hall, Amer. Journ. Sci., ser. i, vol. xxxiii, p. 142, fig. 1. 



Triarthrus beckii, Green, ibid., p. 344. 



1842. Triarthrus becki, Mather, Geol. New York, 1st Geol. Distr., p. 390, fig. 24 (1). 

 Triarthrus beckii, Emmons, Geol. New York, 2nd Geol. Distr., p. 399, fig. 110 (1). 



1843. Triarthrus beckii, Vanuxem, Geol. New York, 3rd Geol. Distr., p. 57, fig. 8 (1). 



1847. Calymene beckii, Hall, Palseont. New York, vol. i, p. 237, pi. lxiv, figs. 2 a — e ; p. 250, pi. lxvi, 

 fi-'s. 2a. — h (non pi. lxvii, figs. 4a — e). 



1848. Calymene beckii, Hall, Amer. Journ. Sci., ser. ii, vol. v, p. 322, figs. 1 a, b, 2 a — g. 

 1855. Triarthrus beckii, Emmons, Amer. Geol., vol. i, pt. 2, p. 214, pi. xv, fig. 12. 

 1858. Calymene beckii, Eogers, Geol. Surv. Penn., vol. ii, p. 820, fig. 613. 



1 Gronwall, ' Bornholms Paradoxideslag ' (Danmarks Geol. Unders., II Baek. Nr. 13 [1902]), 

 pp. ss 91, L01. 



2 Jaekel, 'Zeitschr. deutsch. Geol. Gesell.,' vol. lib, 1901, p. 133. 



