THE FAUNA OF TKB ST. JOHN GROUP. 129 



Ouangondianus, we find as great differences (except in the number of segments in the thorax, 

 which is not known) as are used in discriminating these species of Ellipsocephalus. 



"We seem to see also in the Swedish species of this genus the influence of the habitat, 

 for the species E. poli/tomus and E. NordensJdohli have smooth shields, while the species 

 E. granulatus, in shale associated with a more pelagic fauna, has an ornamented surface. 

 In E. muticus [Liostracus muticus, Aug.), the surface is perhaps only doubtfully known. 



As this genus has been so thoroughly worked up in Europe, and the material repre- 

 senting the Acadian species is so imperfect, it seems preferable to present it without a 



name. 



Ellipsocephalus, sp. ? (PL II, figs. 8 a to c.) 



Only the glabella, occipital ring and fixed cheeks are known. The glabella is some- 

 what defective in front, but appears to have been broad in proportion to its length. It is 

 narrower behind than in front, and is strongly arched from front to back ; it is somewhat 

 ridged along the axial line. Three furrows are faintly indicated on the sides of the 

 glabella ; of these, the anterior is directed forward, the middle one is transverse, and the 

 posterior is arched backward towards the occipital furrow. This furrow is defined by a 

 distinct, but not very marked slope at the back of the glabella, and a fainter slope next 

 the ring. The occipital ring is somewhat rounded downward behind, and is narrower 

 and more strongly arched transversely to the axis of the body than the glabella. The 

 fixed cheeks are not separated from the glabella by a distinct dorsal furrow, but by a 

 rounded slope, and they continue to slope downward towards the eyelobe. 



Sculpture. — The surface of the test, which is thick and firm, is marked by a minute 

 granulation, only visible with a strong lens. 



Length of the part preserved, 10 mm. ; width, 15 mm. Probable length of the whole 

 shield, 13 mm. ; width, 18 mm. 



Locality and Horizon. — Gray, calcareous sandstone at the base of Div. Ic. at St.Martin's. 



This is one of the oldest trilobites known in the St. John group. The glabella is less 

 distinctly defined from the cheeks than that of E. Hoffi of Bavaria, and the cheeks are less 

 tumid. It appears to resemble E. polytomus more than any other described species. E. 

 Nordenskioldi differs in having a glabella wider behind than in front. Our species occurs 

 just below the layers which carry a fauna similar to that associated with Paradoxides 

 OHandicus in Sweden ; Ellipsocephalus polytomus and E. Nordenskioldi are therefore the 

 Swedish species which homotaxically stand nearest it. No examples of the genus have 

 yet been found at higher levels in the St. John group of Cambrian rocks. 



II.— PTYCHOPAEID^. 



AGRAULOS, Hawle & Corda (184*7.) 



ARIONELLUS, Barrande (1852.) 



The description given by Corda does not very clearly express the characteristics of the 

 genus ; but as the genus appears to have been founded on A. ceticephalus, Corda's name 



Sec. iv, 1887. 17. 



