F. R. Cou'per Reed — On Phacops Weaveri, Salter. 69 



V. — Notes ois Phacops Weaveri, Salter, 

 By F, R. CowpER Reed, M.A., F.G.S., Sedgwick Museum, Cambridge. 



ARE-EXAMINATION of the type-specimens of Phacops Weaveri, 

 Salter,* in the Museum of Practical Geology, Jermyn Street, 

 was recently rendered necessary in connection with my palaeontological 

 work on the Tortworth Silurian area, the results of which have been 

 published in the November number of the Quarterly Journal of the 

 Geological Society, 1908 (vol. Ixiv, pp. 512-545), in a joint paper by 

 Professor S. H. Reynolds and myself. A question had arisen in the 

 course of our work as to the occurrence of this species above the 

 Llandovery Beds, for Salter had stated that some of his figured 

 specimens of pygidia (Mon. Brit. Trilob., pi. iii, figs. 2, 3) came from 

 doubtful Ludlow rocks at Horse-shoe Farm, Tortworth. The species 

 had, however, been founded by him previously on specimens from so- 

 called ' Caradoc ' [ = Llandovery] rocks from Long's Quarry, Tortworth,^ 

 and an outline figure of the pvgidium, apparently a restoration based on 

 the three specimens in Jermyn Street (Nos. 19220, 19221, 19222), had 

 then been given. Subsequently a head-shield from the same quarry 

 was figured in his monograph (pi. iii, fig. 1). It is clear that Salter 

 based the species mainly on the pygidial characters, for the head- 

 shield is dismissed with a few inadequate remarks, its resemblance 

 to Ph. caudattis being considered to be very close. The original 

 description given by Salter in 1849 runs as follows: — "P. laevis, 

 capite quam in P. caudato, nisi lobis glabellae tumidioribus ; — cauda 

 triangulari, fere aequilatera, convexa, apice acuto baud mucronato, 

 axi 13-16 annulato, costis lateralibus 10-12, simplicibus, vix curvatis, 

 ad marginem aequalem angustum abrupte terminatis." In the 

 diagrammatic figure of the pygidium which accompanied this de- 

 scription only 12 or 13 rings are indicated on the axis and 10 or 11 

 ribs on the lateral lobes, which might incline us to think that an 

 immature individual was chosen for the figure, since Salter in his 

 remarks on the species says (op. cit.) that "young specimens have 

 not the full number of ribs ", bat no mention that this is the case is 

 found in the explanation of the plate. In Salter's subsequent work 

 (Mon. Brit. Trilob., p. 58) the tail is described as "broad-triangular, 

 wider than long; the sides a little convex; the apex short-mucronate; 

 the axis narrow, conical, ribbed by about sixteen rings ; the sides very 

 convex with nine to ten arched simple ribs scarcely at all interlined ; 

 the margin [ = border] narrow, smooth ". The italics in this quotation 

 are mine, as the number of ribs is fewer than that given in his earlier 

 definition of the species. It may here be remarked that Salter in his 

 . monograph reproduces verbatim the definition of the species published 

 in the decades, with the addition of the word trigono with reference 

 to the head before the word nui, and with the insertion of the epithet 

 muUicostata after the word csquilatera in the description of the 

 pygidium. 



i Salter, Mem. Geo!. Surv., 1849, dec. ii, art. 1, p. 7, pi. i, fig. 16 ; Mon. 

 Brit. TrUob., 1864, p. 57, pi. iii, tigs. 1-3 ; pi. iv, figs. 6-9. 



2 The site of this quarry in the Llandovery rocks has been fixed with much 

 probability by Professor Reynolds (op. cit., p. 514). 



