APTYCHOPSIS LAPWORTHI. 107 



preserved in most of the examples, and in two cases the cephalic plate is retained. 

 The best specimen (fig. 9) has this plate in place, but the edges of the notch have 

 been shghtly damaged and disturbed by pressure, so that its angularity is some- 

 what modified. The angle of the nuchal suture is about 60°. In outline the 

 valves are shorter and fuller (more convex) on the posterior outer margin than in 

 A. prima, and therefore correspond to fig. 17 in Barrande's plate, and which we 

 separate from jjrima and its var. secunda. 



PI. XV, fig. 7, a left valve, with trace of a right. | , 12 mm.; — , 9 mm. ; 

 A, 6 mm. at 45°; ^_,, 9 mm. ; I, 6 (?) mm. ; V, 90°. The two valves broadly 

 sagittate. Carapace oval. In dark-grey thin mudstone, very finely micaceous. 

 Valve structureless, black film ; no concentric lines, but roughly impressed by the 

 minutely concretionary surface of the stone. From the Grieston Shales of the 

 Gala group at Inverleithen, above the Moffat group, and equivalent to the upper 

 part of the Middle Silurian. Coll. Lap worth. No. 59620, British Museum. 



PI. XV, fig. 3, two valves, narrowed by crush. | , 10 mm. ; — , 3 mm. ; 

 A, 4 mm. at 60° (?) ; ,_^, 4 mm. ; I, 4 (?) mm.; V, 60° (?). The two valves 

 subsagittate. Carapace in present condition narrow ; oval or elliptical. 



This specimen has been narrowed by lateral pressure acting obliquely across 

 the long axis of the shield, as is indicated by imperfect cleavage-planes crossing 

 the modified test at an angle of about 60°. The frontal notch has been narrowed 

 and its sides made unequal. 



In hard black mudstone, much like that of Rebecca Hill (PI. XV, fig. 2). Valves 

 somewhat pyritous, modified by cleavage-pressure almost at right angles to the 

 long axis of the valves. Graptolitic mudstone. No. 9, Skelgill beds ; Skelgill 

 Beck. Coll. Marr. Woodwardian Museum, Cambridge. See Catal. Type Fossils 

 Woodw. Mus., 1891, p. 133. 



What seems to be a similar example of a modified Aptychopsis, squeezed into 

 an even narrower and more lanceolate shape, has been figured by Mr. James 

 Dairon in the ' Transactions of the Geological Society of Glasgow,' vol. vii, part i, 

 1883, pi. vii, fig. 35, and referred to in the explanation of the plate as " Discino- 

 caris Broioniana, var. ovalis," Dairon.^ 



PI. XV, fig. 10. Two valves flattened and imperfect. | , 10 mm. ; — , 4 mm. ; 

 A,4mm.at60°; ^_^,3mm.; I, 4 (?) mm. ; V,60°(?). The two valves subsagittate ; 

 carapace elliptical. In black, finely micaceous shale. Valves thin, flattened, and 



^ All the little Phyllopod tests figured in this pi. vii are from Moifat (p. 177), and, excepting 

 fig. 29, are termed " Discinocaris Browniana" by Mr. Dairon ; but most of them appear to belong 

 to other genera. Fig. 29 is Peltocaris Carruthersii. Figs. 31 and 34 are round shields of probably 

 Aptyehopsis glabra, H. W. Fig. 35 seems to be a specimen of A. Lapivorthi much narrowed by 

 pressure. Fig. 32 is probably a broad Aptyehopsis, like A. ohlata ; if it be really a Discinocaris 

 (D. undulata ?) it should not have the dorsal suture. 



