530 Frof. C. Lapivorth — On Olenellus Callavei. 



The fragments figured on Plate XIV. are those which were 

 exhibited by myself at the meeting of the Geological Congress at 

 London in 1888, supplemented by a few others which were at the 

 time in my possession. The majority were collected by Mr. H. 

 Keeping (acting under my instructions with the kindly consent of 

 Prof. T. McKenny Hughes, F.R.S.) during the previous years, and 

 are the property of the Woodwardian Museum, Cambridge, 



The restoration attempted on Plate XV. is founded essentially 

 upon these fragments ; so that palgeontologists will be able to 

 judge for themselves in what respects that restoration is justified 

 or defective. 



Olenellus (Holmia) Callavei, Lapw. 



Plate XIV. Figs. 1-25. Plate XV. Fig. 26. 



1888. Olenellus Callavei, Lapworth, Geological Magazine, Dec. III. Vol. V. 

 p. 485. 



1888. Ibid. Lapworth, "Nature," vol. xxix. p. 213. 



1889. Olenellus Callavei, Walcott, American Journal of Science, vol. xxxvii. p. 391. 

 1891. Olenellus {Holmia) Callavei (Lapw.), Walcott, "Fauna of the Olenellus 



Zone," 10th Report Geol. Survey, U.S.A., pp. 640-641, p. 581, etc. 



Description. — General form ovate-elliptical, about one and a half 

 times longer than broad. Head broad, semi-circular to semi-elliptical 

 in outline and moderately convex. Margin edged exteriorly by a 

 broad conspicuous rounded rim or flange, and limited interiorly by 

 a faint parallel angular ridge. Posteriorly the margin is broadened 

 and prolonged in a strong rounded spine. The under side of the 

 proximal margin forms a broad rounded doublure. The posterior 

 margin of the head bears two short, stiff, spur-like " interocular " 

 spines, which are directed backward and outward, and are continued 

 interiorly by a faint ridge which appears to be prolonged almost to 

 the crest of the glabella in advance of the occipital furrow. 



Glabella broadly convex in elevation, and sub-clavate in outline ; 

 attaining its greatest width near the anterior extremity of the eye- 

 lobe, and having a sharply rounded to sub-triangular frontal edge. 

 It is furnished with three pairs of glabellar furrows (with traces of 

 a fourth anterior pair). They occur as shallow and broad double 

 depressions, deepest midway between the axis and the lateral 

 margins, and almost disappearing as they cross the central parts 

 of the glabella. Occipital furrow of the same type as the rest ; but 

 broader and deeper, and limited in part anteriorly by a slight but 

 conspicuous ridge (the proximal extension of the "interocular" 

 process?). Occipital ring flat and nan-ow laterally; rising posteriorly 

 to a strong marginal rim, and rapidly increasing in width and height 

 to its centre, where it insensibly graduates into a stout claw-like 

 spine, which arches backward over the first two (?) segments of 

 the thorax. 



Eye-lobes prominent, elongate, narrow, lunate to semi-circular, 

 situated sub-centrally with respect to the height of the glabella ; 

 arching outward from the base of the anterior lobe to a distance 

 equal to half the width of the glabella, and backwards almost to 

 a line with the occipital furrow. Visual surface unknown. Area 



