130 G. F. MATTHEW : ILLUSTEATIONS OF 



should have precedence of Arionellus, Barrande. Besides the species which more clearly 

 approach the type, as A. longicephalus, Hicks, of Wales, aud the two described by Billings 

 from Newfoundland {A. socialis and A. affinis), a number of other forms, departing consider- 

 ably from the type have been described under this genus or its synonym Arionellus. 

 Besides A. difformis, Angelin, of Sweden with a long eyelobe, and variable front limb 

 separated from the cheeks, A. strenuns. Bill., of Newfoundland with long eyelobe aud 

 channel in front of the glabella and cheeks, A. quadrangularis, Whit., of Massachusetts 

 with long glabella, and devoid of an occipital spine, and A. primœmis, Brogg., of Norway 

 also without a spine, but otherwise like A. strenims ; others have been added which 

 introduce such important varieties from the original basis of the genus, that it becomes 

 necessary to divide it, or to give it a wider range of character. The author has, there- 

 fore, placed under it some species of the St. John group, having features which exhibit 

 a leaning towards Ptychoparia, but are distinguished by a comparatively horizontal 

 course to the anterior marginal fold (both of the centre-piece of the head-shield and of the 

 movable cheek) and by a heavy and only slightly-elevated spinous occipital ring. These 

 species have a nearly straight suture, as in Agraulos ; but one has the long glabella, deep, 

 dorsal furrow, and transverse depression in front of the glabella, which throw it into 

 association with A. strenuus, Bill., and possibly with A. difformis, Ang. 



Agraulos (?) Whitfieldianus, n. sp. (PI. II, figs. 1 a to/.) 



Only the centre-piece of the head-shield is known. This is subelliptical, somewhat 

 pointed in front, aud slopes steeply downward, both in front and at the sides. The dorsal 

 furrow is distinct, but only slightly indents the cheeks. The anterior margin is strongly 

 arched forward, and has a flattened fold, from which the somewhat tumid anterior limb of 

 the cheeks rises rapidly to the glabella. The space in front of the glabella is about half 

 as wide as the length of the glabella. 



Glabella. — This is prominent, cylindro-conical, rounded in front, a little longer than 

 wide, marked (in the mould) on the sides by four furrows, of which the two anterior 

 point forward, the middle one is transverse, and the posterior arches backward toward the 

 occipital furrow. The two posterior furrows are distinctly impressed on the outer surface 

 of the test. 



Ocnpilal Ring. — Extends backward in a strong spine, and with this aculeate extension, 

 is about half of the length of the glabella. The occipital furrow is divided from the 

 glabella by a steep slope, but fades away into the ring. 



Fixed Clieeks. — Are somewhat tumid all around the front aud sides of the glabella 

 and descend rapidly toward the eyelobes, which are about as far from the glabella as two- 

 thirds of the width of that part. The eyelobes are rather long, slightly upturned, and in 

 the mould are connected with the front of the glabella by an ocular fillet. 



Posterior Margin. — Is arched backward from the inner end, aud forward from the 

 middle, towards the facial suture. About one-third from the inner end it is slightly geni- 

 culated, and thence descends rapidly to the facial suture. The posterior furrow is wide, 

 especially in the middle, shallow and arched forward at the outer end. 



Facial Suture. — This is short, especially in front of the eyelobe, and behind the eyelobe 

 arches outward and backward to the posterior margin. 



