﻿Yol. 66.^\ THE CAMBRIAN ROCKS OF COMLEY. 23 



Microdiscus Helena, Walcott. (PI. Ill, figs. 14-16.) 



C. D. Walcott, Proc. U.S. Nat. Mus. vol. xii (1889) p. 40; and 10th Ann. Rep. 



U.S. Geol. Suvv. 1888-89 (1890) p. 632 & pi. lxxxi, figs. 1-1 a. 

 P. Lake, 3Iicrodiscus sp., ' British Cambrian Trilobites ' Monogr. Palaeont. Soc . 



vol. lxi (1907) pt. ii, p. 34 & pi. iii, fig. 8. 

 E. S. Cobbold, JSIicrodiscns sp., cf. helena, Wale. Rep. Brit. Assoc. 1908 



(Dublin) 1909, p. 235, & Mierodisens sp., ibid. p. 237. 



Since Mr. Lake figured the single pygidium from the Olendlus 

 Limestone of the Comley Quarry, additional and better-preserved 

 specimens have been found from the same horizon at the excavation, 

 200 yards to the south. He has kindly examined these, and tells 

 me that he regards them as quite confirming his opinion that 

 Dr. Walcott's species is represented at Comley. 



Three pygidia [385, 386, 387]. in which the test and original 

 convexity are preserved, are figured on PI. III. These show four or 

 five annulations of the axis, in addition to the articulating surface 

 in front and a terminal posterior portion : the side-lobes are con- 

 fluent beyond the end of the axis, and are marked by four impressed 

 lines, which are less strongly shown on the exterior than on the 

 interior. The margin is narrow and convex. The convexity of 

 the shield seems to vary from about \ to 4-, and the surface of the 

 test appears to be smooth. The length is from 2 to 2j millimetres. 



Locality and horizon. — Comley, from the Olenellus Lime- 

 stone of the quarry ; from the excavation 200 yards south thereof ; 

 and from the same horizon at an excavation at the northern end 

 of Dairy Hill, 200 yards to the south-east. 



Microdiscus speciosus, Ford. 



S. W. Ford, Am. Journ. Sci. ser. 3, vol. vi (1873) p. 137 & figs. 2«-2 6 ; and 



vol. xiii (1877) p. 141. 

 C. D. Walcott, U.S. Geol. Snrv. Bull. 30 (1886) p. 154 & pi. xvi, figs. 3, 3 a-c ; 



and 10th Ann. Rep. U.S. Geol. Suvv. 1888-89 (1890) p. 632 & pi. lxxxi, 



figs. 5, 5 a-c. 

 P. Lake, ' British Cambrian Trilobites ' Monogr. Paheont. Soc. vol. lxi (1907) 



pt. ii, p. 33 & pi. iii, fig. 7. 



A good head-shield from my collection has been figured by 

 Mr. Lake in his monograph. 



With the exception of two imperfect and rather doubtful pygidia, 

 no further remains of this species have come to light. 



Locality and horizon.— Comley, from the upper part of the 

 grey limestone, at the excavation 200 yards south of the quarry. 



Ptychoparia, Corda. 



PirCHOPAKIA. (?) ATTLEBOEENSIS, &h. & F. (PI. Ill, fig'S. 11-13.) 



N. S. Shaler & A. X. Foerste, Bull. Mus. Comp. Zool. vol. xvi (1888) p. 39 & 



pi. ii, fig. 14. 

 C. I). Walcott, 10th Ann. Rep. U.S. Geol. Surv. 1888-89 (1890) p. 619 & 



pi. xcv, fig. 2. 



In my collection there are some fifteen or more specimens of a 

 minute cranidium which answers very closely to Dr. Walcotts 



