236 



MESSES. PEACH AND HOENE ON THE 



of the numerous carapaces found, yet all the fragments are marked 

 with a similar surface-ornamentation. This consists of a network of 

 finely-raised lines enclosing polygonal flat-bottomed depressions. 

 Purther, the collection affords carapaces of the dominant species of 

 the proper size to fit these other fragments. The presumption there- 

 fore is in favour of the opinion tha't all these remains helong to 

 members of one species. It is to he hoped that a further search will 

 yield us sufiicient material to clear up this point and will also afford 

 us the means of describing the larger species, the remains of which 

 at present in our possession seem to indicate that its carapace some- 

 times attained a breadth of six inches. The thanks of the Authors 

 are due to Mr. Charles D. Walcott, Prof. Brogger, and Prof. Lap worth 

 for valuable assistance in directing them to the literature bearing 

 upon the subject of Olenellus. 



Genus Olenelltjs, Hall, 1862. 



Before entering on the detailed description of the fossils, it may be 

 fitting to state the view as to the subdivision of the genus adopted 

 in this paper ; it is practically identical with that of Walcott as 

 given in his ' Pauna of the Lower Cambrian or Olenellus Zone," 

 which is as follows : 



I. Olenellus to be restricted to such forms as have the character 



istic Olenellid carapace and styliform telson, the type of 

 which is 0. Thom^soni, Hall, and including the species 

 0. Gilbcrti, Meek, 0. Iddingsi, Walcott, and 0. Walcotti, 

 Schaler and Poerste. 



II. Mesonacis.^ To include those forms with Olenellid carapace, 



Paradoxidean pygidium, and with greatly produced spines 

 upon the central lobes of one or more of the body- or ab- 

 dominal segments. Type : — Mesonacis vei^moniana, Hall, 

 including M. asa])lioides^ Emmons, and M. MicJcwitzi, 

 Schmidt. 



III. Holmia.^ To include those forms that have the Olenellid 



carapace with Paradoxidean pygidium, and a row of spines 

 down the centre of the axis of the body-rings and the 

 occiput, the occipital spine being often greatly elongated. 

 Type : — Holmia Kjerulfi, Holm, including H. Broggeri, 

 Walcott, and H. Callavei, Lapworth. 



It is in this restricted sense that the generic term Olenellus is 

 here used. 



Olenellus Lapwoethi, nov. spec. PI. Y. figs. 1-11. 



Carapace in a general way semicircular, but varying in different 

 individuals, from the length being sometimes more and some- 

 times less than half the breadth. On the dorsal aspect it is 



1 Tenth Annual Eeport U.S. Geol. Survey, 1888-1889, pp. 633-635. 



2 Walcott, Am. Journ. Sci. vol. xxix. (1886) p. 328, figs. 1 & 2. 



^ Matthew, Trans. Eoy. Sec. Canada, vol. vii. sec. 4 (1889), pp. 136-162. 



