DITHYROCARIS TRICORNIS. 173 



segments, and a trifid caudal a^jpendage, project from the lower part of the front 

 of the carapace. 



The test was sufficiently thin (probably by the loss of the external layer) to 

 allow of the_ gastric teeth being exposed, together with some other (obscure) 

 internal organs. 



There is also a curved object standing out at the antero-dorsal region, and 

 continued backwards into the cephalic i-egion with a straight (somewhat solid, but 

 apparently broken) stem. Whether it be a disconnected portion of the margin, 

 or quite adventitious, is doubtful. 



The thick and double ventral margin is brought out in relief, with its strong, 

 flat, triangular spine. 



The dorsal edge of this (the right) valve is distinct; possibly tuberculated 

 anteriorly, and decidedly marked on its posterior third with a row of oblique 

 striiB or close-set prickles, pointing backwards ; and though similar to the fringe 

 usually present on the ventral edge, it is the side view of a dorsal ridge or crest 

 of sharp, chevron-like rugge, and ends in a strong, flat, triangular spine, such as 

 is seen in the allied species, D. Golei, PI. XXIII, fig. 1, and PI. XXIV, fig. 4, 

 though not so strong. Another posterior spine of the carapace stands out below 

 that of the dorsal margin (between it and the ventral spine), and makes the third 

 " horn " of Scouler's D. tricornis. This latter spine is probably that of the left 

 valve, which (as seen through the thin and compressed carapace) has been 

 shifted, and broken along its mesolateral ridge. 



This fossil has been described and figured in the ' Geological Magazine,' vol. x, 

 pp. 483, pi. xvi, fig. 2. It was found one mile east of Paisley, Renfrewshire, 

 in the same black, thin-bedded earthy limestone from which Dr. Scouler's D. 

 testuJiiiea (PI. XX-IV, fig, 7) was obtained. Both of these unique specimens 

 have been lent to us for illustration and description by the Trustees of the 

 Andersonian Museum in Grlasgow. 



PI. XXII, figs. 5 a—e. Dunn Coll., C 14, 29. Redesdale. 



Size. — A fragment 50 mm. long by 27 mm. broad. The whole valve was 

 probably more than 65 mm. long and 30 mm. broad. 



Characters. — The antero-dorsal portion of the front end has been broken away, 

 leaving a small part of the antero-ventral region, which retains an indication of 

 the approximately real curvature of that portion of the ventral border. The 

 straight edge of a portion of the middle of the crested dorsal border is evident 

 (compare fig. 6, PL XXIV), and was probably continued forwards (upwards in 

 the plate). A relatively long, sinuous, rugose nuchal ridge lies near the front end 

 of the dorsal line, and joins on (with a curve) to the \ong, thin, rugose, juxtadorsal 

 ridge, parallel to and inside the dorsal edge (just as in fig. 1, PI. XXIV). A curved 



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