G54 ^Ii. T. II. Withers 07i 



slightlv near the inner margin, to fit under the inturneil 

 niariiins of the plates of the right-hand series, thus forming 

 a kind of hinge (see PI. X. fig. 4). In consequence of the 

 tapering of the shell at each extremity, the plates vary some- 

 what iu shape according to their position in the shell, but 

 there is also much difference in the shape of the plates, 

 their number, and ornament, in the different species. On 

 the inner surface of each phite of the two columns, near the 

 middle, there is a well-marked sub-circular muscle-scar. 

 Genotype. — L.jamesi (Ilall & Wliitfield). 



Lepidocoleus grayce, sp. n. (Pi. X. figs. 1-5.) 



1908. Aniielidan Tube (?), Cowper Reed, Geol. Mag. dec. v. vol. v. 

 p. 295, pi. xii. fig3. 9, 10. 



Diagnosis. —K Lepidocohus with more than 10 plates in 

 a column, a length of more than 25 mm., and a breadth of 

 5 mm. : plates overlapping to almost half their length, 

 mostly about twice as wide as long, with an ornament of 

 comparatively wide-spaced growth-ridges, about four to a 

 millimetre, and of five to six very slightly finer ridges 

 Ijctweeu each main ridge, giving the surface, where well- 

 preserved, an exceedingly closely and regularly ridged 

 appearance. 



Hurizon and hcaVitg. — Upper Ordovician, Lower Ard- 

 millau series, Drummuck group, Mudstones: Thraive Glen, 

 Girvan, Ayrshire. 



Collection. — Geological Department of the British Museum 

 (Mrs. Robt. Gray Coll.), registered In. 21648 and In. 21649. 



Holotype. — The specimen (In, 21648) figured, PI. X. 

 figs. 1-4', which is presumably the specimen partly figured 

 by Cowper Heed (1908, figs. 9, 10). 



Material. — Two incomplete shells with the plates very little 

 displaced. 



Description. — One specimen (PI. X. fig. 5) represents a 

 shell, including the basal extremity; its length is 20*4 mm., 

 and its greatest breadth 50 mm. This shell is bent or 

 humped, with the result that the plates are somewhat tele- 

 scoped and displaced ; the shell-layer of the plates has been 

 removed in places, so that only the impression remains. 

 At least sixteen plates or their impressions can be counted 

 in serial order, but, owing to the bad preservation, the form 

 of the j)late at the base cannot be made out, although the 

 rounded shiny impression on the matrix leaves no doubt 

 that this really is the rounded basal extremity. Both this 



