Vol. 69.] OF THE COM1EY BEECCIA-BED. 37 



flat, and having a width equal to about a seventh of the length 

 of the shield, omitting the spines ; armed on each side with six 

 spines, which are somewhat hooked at their terminations, and 

 decrease in size from front to rear ; in front of the anterior rib 

 of the lateral lobe where it crosses the border there is a shoulder- 

 like expansion or facet; posteriorly, and immediately upon the 

 axial line, the border is crossed in the smaller specimen (PI. Ill, 

 fig. 15) by a slightly raised riblet, a very faint trace of which is 

 also to be detected on the largest [1819] (fig. 13). 



Test. — No specimen of the pygidium is sufficiently well pre- 

 served to show the surface-characters. 



The species differs from the other form of the genus from Comley 

 {Doriipyije lalcei Cobbold) 1 : (1) in having a rather longer eye-lobe ; 

 (2) in being proportionately wider across the posterior angles of the 

 cranidium ; (3) in the surface-characters ; (I) in the proportionate 

 length of the spines : (5) in the presence of pleural facets, no traces 

 of which have been detected in D. lalcei ; (6) in the more tapering 

 axis of the pygidium ; (7) in the absence of spines on that axis ; 

 and (8) in the diminution backwards in the length of the marginal 

 spines. 



No trace of a pit on the line of the axial furrow, such as that 

 which is so noticeable in J), lalcei, has been detected in D. reticulata. 



The cranidia of the two species are very much alike, but the 

 thorax and pygidia are decidedly different, and the reticulate 

 ■character of the test, when it can be observed, is very distinctive. 



Microdiscus. 



Miceouisces punctattjs Salter. 



J. W. Salter, Q. J. G. S. vol. xx (1864) p. 237 & pi. xiii, tig. 11. 

 P. Lake, ' British Cambrian Trilobites' Monogr. Pal. Soe. vol. lxi (1907) pt. 2, 

 p. 36 (where full references are given) & pi. hi, figs. 11-17. 



Of this form, only one specimen has been found [1471] in the 

 Breccia-Bed. It consists of the concave interior of a cranidium, 

 with some of the calcareous rock-matrix adherent in places. 

 Those portions of the interior of the test which are clear of this 

 matrix show distinctly a regular series of punctations, apparently 

 uVep enough to pass quite through the test. Mr. Philip Lake, who 

 kindly examined the specimen, observes (in litt.) that 



• the crenulation of the margin does not look so fine and regular as is usual in 

 M. punctaius. But possibly the nature of the matrix may have something to 

 do with the difference in the appearance.' 



1 Q. J. G. S. vol. lxvii (1911) p. 287 & pi. xxv, figs. 1-8. 



