[MATTHEW] STUDIES ON CAMBRIAN FAUNAS 7S 



TKILOBITA. 



MICRODISCUS, Emmons. 

 MicRODiscus BELLiMARGiNATUS, Staler and Foerste. 



M. bellimarginatus , S. and F., Mus. Conip. Zool. Cam., Bull., 1888, vol. xvi., No. 2, 

 p. 35, pi. 2, figs. 19a and b. 



Mut. iNsuLARis, n. mut. 



A number of the head and tail shields of this species were found in 

 the gray calcareous shale of a railway cutting at Manuel. 



The mutation indicated differs from the type of Shaler and Foerste 

 in having a narrower head and pygidium, and fewer tubercles on the 

 marginal rim of the head-shield. The shape corresponds more nearly to 

 that figured by Walcott, but the tubercles of the rim are more widely 

 set, and the glabella is more depressed behind than in his examples. On 

 the under side of the border of the pygidium are a series of short spines 

 directed downward that are spaced to correspond to the tubercles of 

 the rim of the headshield. Adjusted to each other they would form a 

 means of locking the two shields together, without the need of absolute 

 contact of the rims of the shields. The tubercles at the side of the 

 head-shield are about a millimetre apart. 



Sculpture. — The surface of the test when viewed with a lens is seen 

 to be minutely granulate. 



Size. — The largest bead-shield observed, was 7 mm. long, and of 

 about the same width. Shaler and Foerste indicate one of 8 mm. 



Horizon and Locality. — Greenish gray calcareous shale of No. 3 

 Walcott section at Manuel's Brook. Protolenus Zone. 



AGRAULOS, Corda. 



Subgen., STRENUELLA. 



Trans. Roy. Soc. Can., vol. iv., pt. iv., p. 153, figs. 3, 3a and b. 



This diff"ers from the typical form of Agraulos {A. ceticephalus), in 

 the elevated glabella, heavy groove across the shield in front of the gla- 

 bella, and long, or continuous eye-lobes ; the posterior marginal fold (and 

 therefore the pleura) is sti-ongly geniculated. Agraulos difformis, acu- 

 leatus and excavatus of the Upper Paradoxides beds in Sweden aj^pears 

 to be a later development from this stock ; these differ from the earlier 

 ones in having a shorter eye-lobe, and longer posterior extension of the 

 dorsal suture. Further remarks in reference to this sub-genus will be 

 found in Transactions of the Royal Society of Canada, vol. iv., pt. iv., 

 p. 154. 



