Notes on Caiiihrian F<(ini(t.s. — Jffiff/ietr; 29 
It is otherwise with the occipital spine, i'or in all the spe- 
cies of the Olenellus zone this is only an obtuse protuberance 
including the last lobe of the glabella and the occipital ring, 
most pronounced in M. hehuia ; but in the Eodiscus section, in 
the Paradoxides zone, the length of this spine bears a direct 
relation to the special sub-zone in which the species is found. 
Thus precursor and sxecicus are found in the Eteminicus 
(^rugulosus) t^nh-zone, jJidcheUus in the Abenacus (i^Tess- 
ni)sub-zone, imnctatas and euceiifriis in the Davidis sub-zone. 
All the long spined species may be said to belong to the 
Paradoxides fauna, but the species with blunt o.cipital rings 
to the Olenellus fauna: and of the species of the Paradoxides 
beds, those which bore the longest spines appeared latest. 
The following scheme will show how the species of Micro- 
discus are related to each other: 
Genus Microuiscus. 
Section, lobatus. Long glabella, occipital ring obtusely pointed. 4-6 
rings in the pygidium. 
r., I, \ M. lobatus Hall, M. meeki Ford. 
Olenellus ^one - tt , -tut , ir 7 7 wj 1 
I M. parkeri Wale, M. heie)ia Wale. 
Section, speciosus. Long glabella, occipital ring obtusely pointed. 10- 
12 rings in the pygidium. 
Olenellus zone, M. speciosus Ford, M. bellicinctus S. & F. 
Section, Dawsonia. Short glabella, occipital ring spined. 6 rings, and 
lateral costa in the pygidium. 
Paradoxides zone, M. dawsoni Hartt, M. sculpius Hicks.* 
Section, Eodiscus. Short glabella, occipital ring pointed or spined. 
o, — 6-12 rings in the pygidium. 
Olenellus zone, M. schucherti n. sp., occipital ring pointed. 
y M. connexus Wale, " " spined. 
h, — Pygidium unknown. 
Paradoxides zone 1 M. precursor lA-Ait., ouc\\)\X:a\ ring, 
(P. eteminicus, sub-zone. I ) with short spine. 
Pygidium with 10-12 or more rings, long occipital spine. t 
(P. eteminicus. sub-zone.) 1 M. suecicus Linrs., M. pulchcllus 
(P. abenacus, sub-zone. ^ ) Hartt. 
(P. davidis, sub-zone,) M. puneitatus Salt., M. euceutrus Tjiiirs. 
Yote on the two species of the Olenellus zone. 
Through the kindness of Mr. Chas. Schuehert I received 
several years ago a number of fossils obtained from the Ole- 
*Dr. Hicks does not figure or mention an occipital spine as existing in 
this species. On account f)f the associated fauna and the resemblance 
to M. (bnrsoiii, I assume that it had one. 
fLinnarssoii's figure of M. suecicus does not represent this spine, but 
his descrijition iiiifiiies that this species possessed a spine. 
