part 4] Cambrian horizons of comley. 329 



Two specimens [2133, 2134] l indicate the presence of a form 

 allied to that described by Linnarsson from the Paradoooides- 

 forcliammeri Zone of Scandinavia. Thej' are not sufficiently well- 

 preserved to be identified with certainty. 



A ventral valve is semicircular in outline, and has the apex 

 recurved to a point beyond the posterior margin. The shell is 

 corneous, dark, and shows radiating riblets crossed by very fine, 

 impressed, concentric striae, which strengthen in places to con- 

 centric rugosities. 



Dimensions. — Length = 2 mm.; width at about the half 

 length = 2*5 mm. ; height = 1 mm. 



Locality and horizon. — Comley, Middle Cambrian; from 

 the JBillingsella Beds, horizon Be. 



Sub-genus Paterina. 

 Micromitra (Paterina) phillipsi Holl. (PI. XXI, figs. 1-3.) 



Obolella phillipsii Holl, 1865, Q. J. G. S. vol. xxi, p. 102, figs. 10 a-10c. 

 Obobella (?) phillipsi (Holl), Davidson, 1866, Pal. Soc. Monogr., Brit. Foss. 



Brach. vol. iii, part 7, No. 1, p. 62 & pi. iv, figs. 17 fl-19. 

 Kutorqina cinqulata Davidson, 1871. Pal. Soc. Monogr., Brit. Foss. Brach. vol. iii, 



pt.' 7, No. 4, p. 312 & pi. 1, fig. 25. 

 Micromitra {Paterina) phillipsi (Holl), Walcott, 1912, U.S. Geol. Surv. Monogr. 



vol. li, p. 351 &pl. iii, fig. 8. 



Through the kindness of Prof. Sollas it has been possible to 

 compare the Comley specimens with those in the University 

 Museum, Oxford (Holl & Groom collections). There can be no 

 doubt as to the reference of the Comley specimens to Holl's species. 

 The forms of the tests and their method of preservation are 

 identical, but thei*e are some points in which the Comley shells 

 exhibit features not seen in the specimens from Malvern at Oxford. 



(1) The external surface often, but not always, shows traces of radiating 



raised lines, as well as the lines of growth ; but the two charac- 

 teristics occupy different parts of the shell, and have not been seen 

 to cross one another as they do in M. sculptilis Meek 2 (fig. 1). 



(2) The line of flexure between the lateral slopes and the false area is 



well rounded, not a sharp angle. 



(3) The false area is almost vertical ; the triangular pseudodeltidium 



is wide ; the angle at its apex (fig. 2, posterior view) is about 

 120° ; it is convex, and extends some distance down towards the 

 posterior margin. 



(4) A well-preserved interior, referred to the ventral valve [2335], with 



the corresponding internal cast [2334] (fig. 3) exhibits numerous 

 radiating shallow channels, and also under the umbo three com- 

 paratively strong ridges, one in an axial position, the others 

 making with it an angle of about 10° on each side. 



The shells are widest at about a quarter of the length from the 

 posterior margin. 



1 The numbers in square brackets are those attached to the specimens in 

 my collection, unless otherwise stated. 



2 C. D. Walcott, 1912, p. 335, & pi. iii, figs. 5 & 5a-5c. 



