J386 F. R. Couyer Reed — Trilobitcs from. HaverfordweHt. 



backwards for a distance at least equal to its length. The points^ 

 of the spines are broken off. Salter {op. cit.) described the genal 

 angles as " short-spinous," but his figured specimens have the 

 angles of the head-shield broken off short, so that their true 

 character could not be determined. 



The whole surface of the head-shield in our specimen is minutely 

 granulated, but the glabella and neck-ring possess also numerous 

 minute inconspicuous tubercles, regularly distributed over the surface. 

 Salter's figures show the head-shield as coarsely tuberculated, though 

 he expressly slates that it is " granular and not tubercular." His 

 figured specimen (op. cit., pi. iv, figs. 5, 6) and other specimens 

 named by him show numerous small low tubercles ; so that the 

 description is misleading. 



Of other species resembling this British form the one named 

 Ch. maxima, Schmidt,' may be mentioned ; the sliape of the glabella 

 and first lateral lobes agrees closely in some specimens, and the 

 proportions as given by Schmidt are similar ; but the presence of 

 distinct second lateral lobes, the more numerous lenses in the eye, 

 and the absence of a tubercular ornamentation mark it off. 

 Dimensions. 



mm. 



Length ot head-sliield 19-0 



Width of head-shield 50-0 



Length of glabella ... .. ... ... ... 15'0 



Width of glabella (anterior end) ... ... ... 25 •5 



Width of glabella (at base) 12-0 



Length of frontal lobe ... ... ... ... 11 "0 



PiiAOOPs (CHASMors) MACROURA (Sjogren) ? (PI. XII, Fig. 3.) 



The second example of the subgenus Chasmops is a specimen of arv 

 imperfect pygidium from the Sholeshook Limestone of the Sholes- 

 hook Railway cutting. It shows the typical characters of the form^ 

 attributed by Salter- to Ch. macronra, Sjogren, but which is believed 

 by Schmidt^ to belong to Ch. Eichwaldi, Schmidt. It appears to me 

 highly probable that the English form is distinct from both these 

 species, and perhaps more than one species has been included by 

 Salter and others under this name. But tlie species of this sub- 

 genus are so closely allied to each other that when dealing with 

 imperfect and fragmentary specimens it is almost impossible ta 

 separate them with certaint}'. 



In this Sholeshook specimen there is a faint row of pits visible 

 along each pleural furrow on the lateral lobes, such as was described 

 by McCoy ^ in the pygidium of Ch. macronra, but this feature was 

 not mentioned by Salter in his specific description and is not 

 observable in the majority of British specimens, though perhaps 



1 Schmidt: Rev. Ostbalt. Silur. Trilob., pt. i (1881), p. 112, pi. iii, fig. 11;. 

 pi. iv, figs. 1-3 (especiallv tig. 2), etc. 



2 Salter: Mon. Brit, trilob., p. 37, pi. iv, tigs. 18-23. 



3 Schmidt: Rev. Ostbalt. Sihir. Trilob., pt. i (1881), p. 117, pi. iv, tig. 4;. 

 pi. V, tigs. 8-10, 16 ; pi. x, fig. 21. 



* McCoy: Syn. Brit. Pal. Foss., p. 162, pi. i G, tig. 20 (O'h)itochlle trimcato- 

 vaudata). 



