DITHYROCARIS COLEI. 165 



Fig. 3. Exposed segments 40 mm. ; ultimate 30 mm. Style 20 mm. Stylet 

 30 mm. 



Fig. 4. Exposed segments 40 mm. ; antepenultimate 6 mm. ; penultimate 

 12 mm. ; ultimate 22 mm. ? Style 22 mm. Stylets broken at tips. 



Owing to the crushed and imperfect state of the several parts these measure- 

 ments are for the most part only approximate. 



Characters. — Fig. 2 shows the same specimen as that represented by fig. 4, 

 pi. xii, of Portlock's ' Report Geol. Londonderry,' 1843 ; with the remains of two 

 abdominal segments and three well-preserved caudal appendages of probably 

 normal characters and proportions ; the dorsal aspect is exposed. The segments 

 are imperfect aud crushed, but the joint between the ultimate and the penultimate 

 supplies a definite datum for their measurement. The ultimate segment bears 

 chevron-lines, with their angles pointing forwards (upwards in the figure). The 

 telson or style is rather shorter than the two cercopods or stylets, and all these 

 are longitudinally striate ; the style, having a median ridge, was bayonet- 

 shaped. 



Fig. 3 is the same specimen as that in fig. 5, pi. xii, op. cit. It has been 

 widened and broken by pressure, so that it is difficult to measure its parts with 

 exactness. It has been mixed up in the shale with a fragment of ventral margin, 

 and perhaps other fragments obscure the ultimate segment, which seems to be 

 broad and chevroned with finer lines than those in fig. 2. The tail-spines are also 

 shorter; but the style is the shortest, as in the other examples. They are sulcate 

 rather than striate, and somewhat granulated on the ridges, a condition due 

 perhaps to fossilisation. Their relative position gives a ventral aspect. 



Fig. 4. The same specimen as fig. 3 a, op. cit., is also flattened and much 

 widened by pressure. The oblique lines on the ultimate segment are directed 

 backwards (downwards in the figure) and inwards towards the centre, thus in a 

 contrary direction to those in figs. 2 and 3. This is the ventral feature in 

 D. testudinea. The three spines may also be said to show their ventral aspect. 

 They are broken at the tips, but resemble those of the other specimens, except 

 that at the head of the stylets a few of the stria? converge at a sharp angle for a 

 short distance — not nearly so far as this feature is continued in fig. 3 a, op. cit. 



The surface of the segments bears patches of an attached kind of Spirorbis 

 (fig. 3 b, op. cit.) ; minute, discoidal, and smooth ; perhaps near Sp. pusillus, 

 Martin. 



PI. XXIV, fig. 2. Mus. Pract. Geol., 6263. 



Size. — Carapace flattened out and imperfect (the same as Portlock's pi. xii, 



fig. 1). Originally about 85 mm. long and 70 mm. wide And 



PI. XXIV, fig. 4. Mus. Pract. Geol., 6262 (bis). Cat. M. P. G., 1865, p. 116. 



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