FAUNA OP THE ST. JOHN GEOUP. S9 



though it is different both iu form aud size. It is ouly about two-thirds of the size of 

 that species, aud is more prolouged in front. The dorsal valve also is ovate, not oblately 

 orbicular as in the type. 



The sculpture consists of concentric ridges, which appear creuulated, owing to inter- 

 rupted, faint, radiating ridges that transverse them. At intervals there are stronger con- 

 centric lines marking stages of growth. The ridges are not so sharply marked as in 

 L. Slarri, and the shell is much thinner. 



Size. — Length of the ventral valve, 11 mm.; width, 9 ram. The dorsal valve is 1 mm. 

 shorter. 



Horizon and Locnlib/. — From slaty layers iu grey flags of Div. 2 at Long Island, 

 Keunebecasis Eivcr. 



This species is near the size of L. lepis, Salt., aud like it is sharply acuminate, but it 

 is a longer shell and has not the sharply striate surface of that species. None of the 

 species of the Potsdam Sandstone described by Prof Hall agree with this form. 



AO-NOSTUS, Brongn. 

 Agnostus pisiformis. L. var. (PI. XIII, figs. 1 a aud b.) 



The following diagnosis of this species is from TuUberg's " Agnostus Arterna " : — 



Crusta laîvis. Limbus non angustus. Caput rotundatum, latum. Frons non louga, 

 biloba. Lobus anterior rotuudatus. Lobus posterior s^^pra medium puncto elevato 

 ornatus, postice rotuudatus. Lobi basales subtriaugulares. Grenœ ante frontem linea 

 separatœ. Pygidium latum rotundatum, bideutatum. Rachis liueolis vix visibilis tri- 

 articulata, postice fere rotundata. Articulus médius postice puncto elevato prœditus. 

 Lobi latérales pone rachin non separati, postice angustati. 



Long, et lat. clypeorum, 5 mm. 



TiiUberg- comments on this description as follows ; — Crust smooth. Border fold 

 rather broad, furnished with two spines on the pygidium. Glabella two-lobed ; the for- 

 ward lobe rounded ; the back lobe with a tubercle in front of the middle ; basal lobes 

 rounded triangular. Cheeks divided in front of the glabella by a furrow. Pygidium 

 broad, rounded. Rachis not plainly articulated, equal sized, almost rounded behind. The 

 middle joint furnished on the middle with an elevated poiut. Side lobes not divided 

 behind the rachis. 



These descriptions agree fairly well with an Agnostus which occurs in the shales 

 north of the flags of Division 2 on Long Island, but not entirely, nor does the species 

 entirely agree with the figures of Linnarsson ' and Tullberg- 



Our variety has a more distinctly lobed rachis in the pygidium and a larger tubercle 

 or point on the middle joint ; the third joint also is narrower and more tapering. 



Size. — Only a few individuals of the size of o mm. to each shield were found, but a 

 large number of about half the length aud smaller. 



Horizon and Locality as stated above. 



^ ' Om Vestergotlands Camb. och Silur. aflag.' Taf. ii, fig. 50 and 51. 

 '•' ' Agnostus Arterna,' Tullberg. Taf. ii, flgs. 14 a and 14 b. 



