332 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53 



lobe of O. lapworthi is much like that of 0. fremonti [pi. 37, fig. 2], 

 but the relative position of the glabella and frontal border of the 

 cephalon is dififerent, as also the enlarged third segment. O. gilherti 

 [pi. 36] has a larger eye lobe than 0. lapworthi, but in other re- 

 spects the two species are very closely related. It is also interesting 

 to note that 0. intennedius Peach [1894, pi. 32, fig. 7], a form that 

 I think is the young of 0. lapworthi, has antero-lateral angles on 

 the cephalon not unlike similar angles on the young cephalons of 

 O. gilherti [pi. 36, figs. 11-14]. 



In the synonomy of 0. lapworthi I have included 0. intermedins 

 Peach and O. lapworthi elongatus Peach. The first I regard as a 

 young cephalon preserving the antero-lateral angles that subsequently 

 disappear, and the advanced genal angles and small eyes that are 

 so well shown by the young of 0. fremonti [pi. 37, figs. 11-12]. 

 The variety elongatus appears from the specimens to be the result 

 of elongation by slight distortion in the shales. 



A cephalon 26 mm. in length has a width of 44 mm. All of the 

 illustrations on pi. 39 are from photographs of compressed speci- 

 mens in a fine argillaceous shale. 



The hypostoma [pi. 39, fig. 7] is much like that of Pcedeumias 

 transitans [pi. 34, figs. 5-7] in having an ovate body and denticulated 

 posterior and postero-lateral margins. I found one quite young 

 cephalon in the material of the Geological Survey of Scotland [fig. 

 6] 1.5 mm. in length that shows prolonged intergenal spines, elon- 

 gated eye lobes, and segmented palpebral lobes, not unlike those of 

 Elliptocephala asaphoides [pi. 25, figs. 9-10]. 



The surface of the cephalon and thorax is marked by a rather 

 strong network of fine, slightly elevated ridges of the same char- 

 acter as those on 0. reticnlatus [pi. 39, figs. 10, 11], except that the 

 network and ridges are finer. 



0. lapworthi differs from the associated 0. reticnlatus in its larger 

 eye lobe, more finely reticulated surface and minor details mentioned 

 under the latter species. It is the representative on the eastern side 

 of the Atlantic basin of 0. thompsoni of the St. Lawrence province 

 of the western side of the Atlantic. The closely allied O. gilherti is 

 from the Cordilleran trough of western America. 



Formation and Locality. — Lower Cambrian : argillaceous shale 

 interbedded in " Serpulite grit," a coarse, quartzitic sandstone, north- 

 ern slope of Meal a' Ghubhais, 1,200-1,300 (366-396 m.) above Loch 

 Maree, 4 miles (6.4 km.) northwest of Kenlochewe in the west of 

 Ross-shire. Scotland. 



