[MATTHEW] STUDIES ON CAMBRIAN FAUNAS 173 



frons as described by Brogger, which is remarkable for the long rachis 

 of the pygidium. The rachis of the Canadian form is shorter, and the 

 shield possesses a broad, flat border fold. Two rings are faintly indi- 

 cated on the front half of the rachis, of which the posterior is crowned 

 by a small tubercle ; var. nepos, however, has distinct rings in the rachis 

 of the pygidium. 



Agnostus umbo, mihi, mut. (PI. I., tigs. Ga and b). 



Agnostus umbo, Trans. Roy. Soc. Can., vol. iii., sec. iv., p. 71, pi. vii., ligs. 

 8rt and b. 



Agnostus umbo. Fauna of Paradox. Beds of E. N. A., p. 222, pi. xvi., lig.s. 

 ia and b. 



A variety of this species is somewhat common in the limestone bands. 

 It is distinguished from A. umbo type by the very weak marginal fold of 

 the head-shield, while on the contrary the marginal fold of the pygidium 

 is somewhat heavier than that of the typical form. In other respects 

 the two forms are much alike. 



A. parvifrons yar. mamillata of Brogger is near this form, but the 

 rachides of the shields are in higher relief, and it has a heavier marginal 

 fold to the head-shield ; this feature and the longer rachis of the pygi- 

 dium also separate from it Tullberg's A. parvifroiu, form 2. 



The Agnosti which in the St. John (Iroup represent Tullberg's 

 forms 2 and 3 of A. parvifrons, viz., A. parvifrons var. tessella and A. umbo 

 are clearly distinct species ; both the glabella and the rachis of the 

 pygidium have constant differences, and the two forms show no tendency 

 to grade into each other. Form 1 of Tullberg we have not found in the 

 St. John Group. 



Agnostus l^vigatus, Dalman, var. (PI. I,, tig. 7). 



Battus lœiigatus. Daim. Vetensk. Akad. Arsber, p. lad. 

 Agnostus lœvigatus, Ang. Pal. Scand., p. 6, tab. vi., fig. 3. 

 Agnostus lœvigatus, Brog., 1. c, p. 74, tab. v., tig. 6, and tab. vi., fig. 5. 

 Agnostus lœvigatus, Tullb., 1. c., p. 27, tab. ii., fig. 17. 



Agnostus lœvigatus. Faunas of the Paradox. Beds of E. N. America, p. 233, 2:^4, 

 235, pi, xvii., figs. In and b, 'la and b, 3o and b. 



Two heads belonging to a variety of this species have been found. 

 They differ from the examples found at Andrarum, figured by TuUbei'g 

 in having a narrower posterior lobe to the pygidium, and are smaller. 

 A dark line in the shell indicating a thickening of the test, outlines the 

 effaced glabella, and shows its relation to that of A. parvifrons, for it is of 

 the same form. 



Sculpture. The surface is minutely granulated. 



Size. Length and width of head-shield, each 3^ mm. 



Horizon. In limestone band of the gray shales. 

 Sec. IV,, 1897. 10. 



