SHUMARDIA PUSILLA. 41 



As Mr. Raw lias devoted a considerable amount of time to the study of this form, 

 I quote his description and notes from the manuscript which he has supplied tome. 



"Body convex, deeply trilobed. Head without free cheeks. Thorax of six 

 segments and tail of four, both ornamented with lines of tubercles. Surface 

 otherwise smooth. General shape ovate, the greatest width being the back of the 

 head-shield, which, in adults of 4 mm. in length, measures 2*5 mm. ; younger 

 individuals are relatively broader {e.g. in a very perfect individual of 3 mm. the 

 width is 2*2 mm., and a larval form of 1 mm. has a head 8 mm. broad). 



" Head roughly half a hemisphere, but somewhat trapezoidal in outline. 

 Glabella strongly arched behind, flatter in front ; at its middle and narrowest part 

 about one third the greatest width of the head, somewhat broader in the neck- 

 segment, and also broader in front, where two eye-like lobes are outlined by furrows 

 behind them. Axial furrows particularly deep up to and round these lobes, in 

 front of them narrow, shallow, and straight, meeting at a blunt angle well above 

 the anterior border. Neck-segment well defined in front by a transverse furrow 

 over the glabella, rounded, and projecting behind. Halfw r ay between the neck 

 furrow and the eye-like lobes a faint lateral furrow is sometimes seen on either 

 side of the glabella near the bottom of the axial furrows. Cheeks at the sides 

 strongly arched and bent down all round, in front continuing the curvature of the 

 glabella ; bounded behind by the occipital furrow' (the hinder edge of which forms 

 a barely perceptible rim), running at first straight out from the neck-segment, 

 then downwards and backwards to the sharp genal angles, which were perhaps 

 furnished with a fine spine. 



" Thorax of six segments. Axis broad, in front half as Avide again as the pleura?, 

 markedly tapering behind. Pleura? running straight out, their ends, except in the 

 fourth segment, thin and facetted, sharply bent down and back and obliquely 

 truncated behind. Fourth segment stronger than the rest, its pleura? prolonged 

 into spines projecting backwards and inw r ards and as long as the thorax and tail 

 combined. Axial part of each segment forming a prominent ring rising behind 

 into a tuberculate crest ; each pleura rising along its centre into a prominent 

 tuberculated ridge, which descends gently to the front of the segment but is 

 separated from the posterior margin by a furrow. 



" Tail subquadrate or semicircular, straight or a little emarginate behind ; 

 surrounded by a prominent rim which touches the axis behind; segments, four in 

 number, conspicuous both on the axis and the limb, ridged like those of the thorax, 

 and like them provided with rows of tubercles ; the rim also is similarly tubercu- 

 lated. Axis prominent, bluntly tapering, about the same width as the limbs on 

 either side. 



" This description is based on external and internal moulds collected from the 

 Shineton Shales by Mr. Rhodes for the Geological Survey, kindly lent by the 

 Director. 



