344 NATURAL SCIENCE. 



JULY, 



Walcott, in his last great work on the Olenellus-fauna (19), 

 abstains, somewhat generously, from breaking up this important genus ; 

 and most workers will approve his action in the present state of 

 knowledge. Messrs. Peach and Home (24, p. 236) also give a clear 

 grouping of the eleven species already known. Whether Olenellus 

 proper, Mesonacis, or Holmia (18), we find in all a semi-circular head- 

 shield, prolonged into long or short posterior spines ; a glabella of 

 nearly equal width throughout, but often narrowed in front ; large 

 eyes ; and no true facial sutures. The number of thoracic segments 

 becomes of little value, ranging from 13 to 26, and it is interesting 

 to find the characteristic head-shield in conjunction with a styliform 

 pygidium in Olenellus proper, and a Paradoxidian pygidium in 

 Mesonacis and Holmia. The great development and frequent pro- 

 longation of the third thoracic segment is not a constant character in 

 the same species, though its occurrence in any specimen suggests 

 that we are dealing with Olenellus. The surface of the whole test is 

 often seen to be ornamented by a network of fine lines enclosing 

 polygonal spaces, so that even fragments may thus be recognised. 



The above details would be beyond our present purpose but 

 that the search for Olenellus has already assumed vigorous proportions. 

 Professor Lapworth (15) in 1888 announced the first discovery of the 

 genus in the British Isles, near the base of the Comley or Hollybush 

 Sandstone, at the foot of Little Caradoc in Shropshire. The species, 

 O. {Holmia) callavei, has been figured and restored (20), so as to be 

 worthy of its Scandinavian rivals, which its large size, six inches by 

 four inches, practically equals. Professor Lapworth unerringly 

 predicted that the Durness series of Scotland might also reach down 

 to the base of the Cambrians ; and in 1891 Sir A. Geikie (22) 

 announced the discovery of Olenellus in the North-West Highlands. 

 Messrs. Peach and Home have now (24) given us a full account of 

 the occurrence of a new species, O. lapworthi, in dark shales at the 

 top of the " Serpulite Grits," and also in the underlying " Fucoid 

 Beds" (so named from fucoidal casts of worm-burrows) on the Loch an 

 Nid river in the south of Dundonnell Forest, Ross-shire. The tourist 

 was formerly denied access to this rugged deer-forest, and Professor 

 Heddle's kindly meant description of it was sternly excised from the 

 visitors' book at the neighbouring hotel ; but perhaps now the 

 hunters of an invertebrate fauna may occasionally gain admittance. 

 The Geological Survey is fortunately free in this respect ; and we 

 now know that the " Serpulite Grit," the " Fucoid Beds," and the 

 quartzite forming the base of the Durness series, some 680 feet in 

 all, are of Lower Cambrian age, and that "the Precambrian age of 

 the Torridon Sandstone necessarily follows, the quartzites being 

 unconformable upon it." 



It is noteworthy that when Professor Jas. Nicol (3) made his 

 famous statement that the lower gneiss of the Scottish Highlands 

 might have been forced up to form the apparently overlying eastern 



