[MATTHEW] STUDIES ON CAMBRIAN FAUNAS 77 



Size. — Length of the head-shield 16 mm., width of the middle-piece, 

 at the front, 12 mm. ; at the eye-lobes IS mm., at the posterior corners 

 20 mm. 



Horizon and locality. — Eed limestone of Brigus, and the calcareous 

 shales of ISTo. 3 Manuel's Brook (Protolenus Zone). 



This mutation is distinguished from the type by its flattened anterior 

 marginal fold, its larger and more prominent glabella, its occipital furrow 

 indented at the sides, but scarcely in the middle, and its large ej^e-lobes. 



It differs from A. dtfformis, Ang.,' in the sharper anterior marginal 

 furrow, heavier eye-lobe, short occipital spine, longer glabella and direct 

 posterior extension of the dorsal suture. 



I have collected a number of heads of S. strenua (typical) in New- 

 foundland, and find it does not attain the size of this form ; the two 

 occur together both at Brigus and Manuel's, and it may be that when the 

 parts are known the two forms may be found to be independent siDecies. 



It seems probable that fig. la, plate xcvii. of Walcott's work above 

 cited, may be intended for this form, but if so, the anterior margin is not 

 correctly represented. 



Strenuella (?) Attleborensis, Shaler and Foerste. PI, lY., figs. 4a to c. 



Ptychoparia Attleborensis, S. and F., Bull. Mus. Comp. Zoology, vol. xvi., No. 2 



p. 39, pi. 2, fig. 14. 



The following is the description of this species by the above authors : 

 " Head small, often minute ; in the largest specimen, 4 mm. long. 

 The usual size is about 2-6 mm. The glabella is oblong or slightly 

 attenuate anteriorly. The occipital groove is low or indistinct. The 

 occipital ring extends beyond the general posterior outline of the head 

 and apparently forms part of the glabella before it. The glabella is 

 sometimes intersected by faint lateral grooves, of which there are 

 three pairs, the anterior pair scarcely visible. Oftener these grooves 

 are obsolete, and the glabella may, in case the occipital groove is 

 very shght, appear as a continuous undivided body as far as the pos- 

 terior margin of the head. The glabella is always convex, and con- 

 siderably elevated above the general level of the cheeks. There is in 

 some specimens a very slight trace of an ocular ridge, which runs from 

 the anterior end of the glabella laterally, and slightly posteriorly, joining 

 a similar slight trace of the palpebral lobes. The most marked feature 

 of the fixed cheeks is the existence of a depression along their postero- 

 lateral outline. The anterior border is proportionately very broad. 

 About the character of the rim little can be said. Near the lateral 

 margin of the border, or rather near the facial suture, there are some- 



1 Brogger-Paradox. skiferne ved Krekling, Christiania, 1878, pi. iv., figs. 1 to 6. 



