THE FAUNA OF THE ST. JOHN GEOUP. 75 



Horizon and Local iti/. All parts of the St. John Basin, in Div. \.d, from the base 

 upward. 



MiCRODiscus PUNCTATUS, var. PRECURSOR, n. var. (Plate YII. Fig. 13.) 



Only the head shield of this variety is known. This is more triangular than that of the 

 tyi^e. The chief difference is in the median lobe, which is conical, and has a distinct 

 furrow separating the occipital ring from the glabella. The inner margin of the cheek, 

 overhanging the dorsal furrow, is nearly straight ; and the marginal fold of the head shield 

 is very narrow, and very obscurely crenulate. 



Individuals of M. pu/didlus, of the same size, do not exhibit the peculiarities of this 

 form, and it is therefore thought to be a distinct variety. 



Length of the head shield, 2 mm. Widlh, 2J mm. 



Horizon and Localily. In the fine, grey shales of Div. l.r, at Hanford Brook, St. 

 Martin's. Rare. 



MiCRODiscus Dawsoni, Harlt. (Plate VII. Figs. 11a, h and c) 



Acad. Geo., 2nd. Ed., p. G54, Fig. 228. U.S. Geol. Surv., Bull. 10. p. 23, PL II. Fig. 

 3 and 3a. 



This is one of the most characteristic species of the Acadian Cambrian rocks. The 

 head shield in my examples is broadly semicircular ; the glabella and cheeks slope down- 

 ward in front below the level of the anterior marginal fold, which rolls upward in front as 

 a prominent, crenulated, transverse ridge ; while, posteriorly, the glabella extends back- 

 ward into a stout spine, slightly hooked downward at the extremity; the two parts, i.e. 

 the glabella and spine, form together a fusiform axial lobe to the shield, for the spine tapers 

 gradually from the glabella, and the two are nearly in the same plane horizontally. 



The pygidium is proportionately longer than the head shield, and has seven segments 

 in the median lobe, and five in the lateral lobes ; the axial lobe does not quite reach the 

 posterior marginal furrow ; the costa? are strongly directed backward, as on the Welsh 

 M. scul]di(s, Hicks. Our species, however, is strongly granulated on the surface of the tests 

 where it is raised above the general level, but not in the furrows. 



Although the pygidium of our species and that of M. scvlptus are alike, the head shields 

 are quite different ; and, as regards the fusiform axial lobe of the cephalic shield, our species 

 might, with propriety, be compared with Microdis^cus eucentrus, Linrs., of Sweden. 



This species was gregareous, the shields being often clustered on layers of the shale. 



Length of the head-shield (exclusive of the occipital spine), 2i mm. Widlh, 3J mm. 

 Length of occipital spine, 2 mm. Length of pygidium, 3 mm {Width, 3 J mm. 



Horizon and Locality. In the fine, grey shales of Div. l.c, at Portland, at RatclifTs 

 Stream, Simond, and at Hanford Brook, St. Martin's, but nowhere plentiful. 



AGEAULOS, Corda. 



Agraulos (?) ARTICEPHALUS, n.sp. (Plate VII. Figs. 14a and b.) 



The cephalic shield between the sutures is oblong subc^uadrate. Glabella large, long- 

 ovate, somewhat pointed in front, marked by three pairs of furrows, which are directed 



