674 MK. B. N. PEACH ON THE FAUNA OF THE [Nov. 1 894, 



described, except Olenelloides, could easily be produced by exagge- 

 ration or suppression of some of its spines, or by addition to or 

 diminution from tbe number of its body-rings. From Holmia (0.) 

 Kjerulfi (Linnarsson), as a central type, it would require a less 

 amount of modification to produce tbe H. (0.) Callavei (Lapworth) 

 of Shropshire tban the H. (0.) Broggeri (Walcott) of Newfoundland ; 

 and in like manner the Mesonacis (0.) MicJcwitzicn (Schmidt) of 

 Russia than the M. (0.) vermontana (Hall) or M. (0.) asapJioides 

 (Emmons) of America. Further, the species of Olenellus found in 

 the North-west Highlands of Scotland would require less modifi- 

 cation than the Olenellus Thompsoni (Hall) or 0. Gilherti (Walcott) 

 of America. The consideration of these points makes it probable 

 that the dispersal of the Olenellids was from the Old towards the 

 New World. 



EXPLANATION OF PLATES XXIX.-XXXII. 

 Plate XXIX. 



Fig. 1. Olenellus Lapworthi. Underside, with imperfect labrum in place. En- 

 larged 2 diameters. From ' Fucoid Beds,' Meall a' Gkubhais, Ken- 

 lochewe, Koss-shire. M. 408b 11 . 1 



Fig. 2. 0. Lapworthi. Enlarged 2 diameters. Same locality and formation. 

 M. 4078". 



Fig. 2a. 0. Lapworthi. Counterpart of fig. 2. M. 4078 d \ 



Fig. 3. 0. Lapworthi, var. elongatus. Enlarged 2 diameters. Same locality. 

 M. 40S0 d . 



Fig. 4. 0. Lapworthi, var. elongatus. Enlarged 2 diameters. Same locality. 

 M. 4089 d . 



Fig. 4a. 0. Lapworthi, var. elongatus. Counterpart of fig. 4. M. 4089 da , 



Fig. 5. 0. Lapworthi, var. elongatus. Enlarged 2 diameters. Labrum supposed 

 to belong to tbis variety. Same locality. 



Fig. 6. 0. Lapworthi, var. elongatus. Enlarged 2 diameters. Pleuron of third 

 segment. Same locality. 



Plate XXX. 



Fig. 1. Olenellus reticulatus, nat. size. From ' Fucoid Beds,' Meall a' Grhubhais, 

 Keulocbewe, Ross-shire. M. 407fi d . 



Fig. 2. 0. reticulatus, nat. size. Underside of head-shield. Same locality. 

 M. 4104 d . 



Fig. 3. 0. reticulatus. Portion of fig. 2, enlarged, to show nature of ornamen- 

 tation. 



Fig. 4. 0. reticulatus, nat. size. Same locality. M. 4161 d . 



Fig. 5. 0. reticulatus, nat. size. Fragment of head-shield. Same locality. 

 M. 4093 d . 



Fig. 6. 0. reticulatus, nat. size. Underside of right pleuron of third body- 

 segment. Same locality. M. 4103 d . 



Fig. 7. 0. Lapworthi. Enlarged 3 diameters. Third body-segment. Same 

 locality. 



Fig. 8. 0. reticulatus. Last four segments enlarged, to show pleura and 

 rudimentary spines on axes. Same locality. M. 4078 d . 



Fig. 9. 0. reticulatus. Last three segments magnified, to show pleura and 

 spines on axes. Same locality. M. 4109 d . 



Fig. 10. O. reticulatus. Body-segments from the tenth to the thirteenth 

 inclusive, magnified to show pleura and spines on axes. Same locality. 

 M. 4102 b . 



1 These are the registered numbers of the specimens in the List-books of 

 the Geological Survey of Scotland. The M stands for Macconochie. 



