Vol. 52.] FAUNA OF THE KEISLEY LIMESTONE. 431 



Affinities. — The Keisley species L. bulbiceps resembles L. verrucosus, 

 Eichw., in the general arrangement and relations of the different 

 lobes and furrows, but it differs (1) by having a relatively much 

 shorter head- shield ; (2) by possessing a much greater convexity 

 than that species ; (3) by the flattening of the posterior portion of 

 the middle shield ; (4) by the larger size and triangular, instead of 

 elliptical, shape of the basal lobes of the glabella ; (5) by the angle 

 of convergence of the anterior side-furrows of the glabella ; (6) by 

 the concave curvature and greater length of the axal furrows 

 between the middle side-furrow of the glabella and the neck- 

 furrow. 



JS 7 ote. — A hypostome of a Lickas with many points of resemblance 

 to the hypostome of L. verrucosus probably belongs to L. bulbiceps. 

 It is subquadrate in general outline, and is nearly as broad as it is 

 long. It consists of a median swollen rounded portion, subcircular 

 in outline and sharply marked off by a deep furrow from the border 

 above which it is raised. It is notched near its posterior end by a 

 pair of short, deep, oblique lateral furrows which are directed back- 

 wards. Its surface is ornamented with small but distinct tubercles 

 of equal size, arranged with some degree of regularity. The border 

 surrounding this central portion is very narrow in front, but 

 expands at the anterior lateral angles into short, bluntly pointed 

 4 anterior wings,' behind which the sides of the hypostome run 

 back parallel to each other. The border increases in width, and has 

 its edge slightly turned up and rounded as far as the posterior end 

 of the median portion, behind which it expands and has its edge 

 bent downward. This hinder portion of the border is ornamented 

 with a series of striae parallel to the lateral margin. The posterior 

 side of the hypostome is excavated so as to appear forked, and 

 immediately behind the median portion the border attains its 

 greatest width, and is raised into a low prominence. The length 

 of the hypostome is a little over 6 millim. 



Lichas biftjrcatus, sp. n. (PL XXI. fig. 7.) 



It seems inadvisable to regard the pygidium on which this species 

 is founded as belonging to L. bulbiceps, for no species allied to the 

 latter has a pygidium with such characters. The pygidia rather of 

 such species as L. triconica (Dames) and L. margaritifer (Xieszk.), 

 with their forked extremity, approach most closely to it. 



Our pygidium is about one and a half times as broad as long ; its 

 shape is almost parabolic, but it is pointed and forked posteriorly. 



The axis occupies the middle third of the width of the pygidium 

 and extends for nearly half its length. It is strongly convex, and 

 tapers gradually to its posterior end, which is truncate, abrupt, and 

 steep. The articulating ring on the front end is broken off, but 

 there are three rings crossing the axis, the first of which is strong, 

 narrower at the middle than at the sides, and marked off by deep 

 wide furrows behind and before. The second ring is very similar 

 to the first, and the third, which is of more uniform width, is deliued 

 posteriorly only by a faint furrow. 



