202 Sedgwick BInseum Notes. 



species are interesting, for the division of the cheeks into two distinct 

 regions recalls the features of the ' cheek-roll ' and ' cheek-lobes ' of 

 many species of Harpes, as carefully described by Bather* in the case 

 of H. lucco. The marginal row of pits suggests a comparison with 

 that found at the base of the cheek-roll and inner margin of the 

 ' brim ' in many species of that genus, and the ' cheek-line ' with 

 that in S. vittatus, Barr. The distinctive ornamentation of the outer 

 and inner portions of the cheeks is also commonly met with in Harpes 

 and Rarpides, but not in Dionide. With regard to Ermnys, as defined 

 by Gronwall,* we may note the similarity of the main vascular trunk 

 running backwards and outwards with radial branches arising from 

 it, especially on the anterior side, and in E. breviceps (Angelin) there 

 is a somewhat similar row of marginal pits. 



But the reference to the genus Bionide seems beyond dispute on 

 the strength of the large size, many annulations, and other characters 

 of the pygidium which may be compared' with that of D. lapworthi 

 (Eth. & Nich.), D. formosa^ Barr., and B. euglypta, Angelin. The 

 many points of affinity possessed by the head-shield with other genera 

 indicate the intimate relations of Dionide with Harpes, Harpides, and 

 Erinnys. 



In 1875 Hicks* described and figured a trilobite from the Upper 

 Arenig of the St. David's area as TrinucUus Ramsay i. The material 

 was very poor and fragmentary, but a comparison of the types with 

 the head-shields of B. atra leads me to believe that they are identical, 

 and if so Hicks' name must be dropped. The imperfect head-shields 

 on which Hicks based his species show tlie single marginal row of pits, 

 the radially ornamented circumferential region of the cheeks, the 

 pre-glabellar band of the inner region, the 'cheek-line', the main 

 vascular trunk, and the general shape and contour of I), atra, so far 

 as their fragmentary condition allows us to determine. The only 

 difference is the rather coarser ornament of the ' cheek-lobes', though 

 it is likewise very much finer and quite different from that of the 

 'fringe' ( = circumferential region). The greater coarseness seems 

 probably due to the state and method of preservation of the specimens 

 and to the larger size of the individuals which Hicks figured. No 

 other feature of importance is present bj' which we can separate them, 

 and the St. David's 7Ww«c/(??<«i?rtmsffye must undoubtedly be referred to 

 the genus Bionide, and almost certainly to Salter's species. Fearnsides* 

 has mentioned a Bio?iide " closely similar to the B. atra of Ty Ohry " 

 as occurring in tlie Olchfa or bi/idus Shales of the Arenig fawr district. 



EXPLANATION OF PLATE XI. 



Fig. 1. Dionide atra, Salter. Pygidium, elongated and distorted. Ty Obry, 

 Portmadoc. (Probably the specimen figured by Salter, Mem. Geol. 

 Surv., iii, pi. xia, fig. 9.) x 2. 



* Bather, " Harpes bucco " : Eivista Ital. Paleont., xv, pp. 116-20, 1910. 



^ Gronwall, " Bornholms Paradoxideslag " : (Danmarks geol. Undersog., ii, 

 Nr. 13), 1902, pp. 94-98. 



* Reed, Mon. Girvan Trilob. (Palseont. Soc), 1903, pt. i, p. 26. 



* Hicks, Quart. Journ. Geol. Soc, vol. xxxi, p. 183, pi. x, figs. 1, 2, 1875. 



* Fearnsides, ibid., vol. Ixi, p. 623, 1905. 



