THE Fi UNA OF THE ST. JOHN GliOUP. 71 



A. declivis may be compared with the later A. secret its, "Walcott, of the Prospect Moiiu- 

 taiu gToirp, which it resembles in its general form, as well as in having a glabella tumid 

 behind. Neither this variety, nor the type of A. Acadicus, appears to have any very near 

 allies among- the species of the Paradoxides beds of Sweden, known to the author. 



Length, about 1 mm. Width, 3 mm. Cephalic shield, 3 by 3 mm. 



Horizon and Locotitij. Abiindant in the fine dark shales of Div. l.d, at Porter's Brook, 

 St. Martin's. 



ActNOSTUS tessella, n.sp. (Plate VII. Figs. 7 u, ^ and r.) 



Body elongate-elliptical, more broadly rounded in front than behind. 



Cephalic shield semi-elliptical, somewhat wider than long ; high in the middle and 

 posterior part. Dorsal furrow very marked at the posterior two thirds of the glabella, very 

 faint at the anterior third. Marginal fold strongly elevated and the furrow deep and 

 strongly impressed. Glabella cylindro-conical, rounded in front ; the width one third of 

 that of the shield, the length five sevenths of the shield ; the anterior lobe of the glabella 

 is depressed to the level of the cheeks, and almost obsolete ; the posterior lobe i.s cylin- 

 drical, roiinded behind, bounded in front by a straight deep furrow, and bears a small 

 tubercle one third from the front : the two basal lobes are small and inconspicuous. 



The thorax is subrectangalar, emarginate in front at the axis and consists of two 

 segments. The anterior segment bears five lobes, of which the two lateral pairs are globose ; 

 the central lobe is transversely elongated, wider behind than before, and bears a minute 

 tubercle at the axial line. The posterior segment is similar to the anterior, except that the 

 middle lobe is not so distinct, and has no tubercle. 



Thepygidium is semi-elliptical, somewhat wider than long, strongly elevated along the 

 axis, and truncated in front at the lateral thirds. The axial lobe is cylindro-conical, its 

 width is one half of that of the pygidium, and its length more than three quarters ; it 

 bears an elongated tubercle on the axial line at the anterior third, and short furrows indent 

 the sides of the axial lobe, opposite the ends of this tiibercle. The lateral lobes are narrow 

 and diminish in width posteriorly ; they are divided at the extremity of the axis by a 

 furrow connecting the dorsal and marginal furrows. 



This species is easily distinguished from all the preceding by its peculiar glabella and 

 by the crenulated sides of the undivided axial lobe of the pygidium. Its nearest ally amou"- 

 the Scandinavian species appears to be var. nepos (Brog.) of A. purvifrons, Liurs, but the rachis 

 of the pygidium has a difierent shape; the glabella of A. tessella differs from all the forms 

 of A. parvifrons in having a distinct, though faint anterior lobe. A. seclusus, "Walcott, of the 

 Prospect Mountain group, belongs to the same group of Agnosti as A. tessella, and the next 

 species described in this paper. 



Length, 9 mm. Width, 4 mm. 



Horizon and Locality. In the fine dark shales of Division l.d, at Porter's Brook, St. 

 Martin's. Common. 



Agnostus umbo, n. sp. (Plate VII. Figs. 8a. and b.) 



Body elliptical, broader in front than behind, high at the inner side of the head and 

 tail shields, descending thence to the front and back. 



