24 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 57 



SIDNEYIA INEXPECTANS, new species 



(PI. 2, figs. 1-3; pi. 3, figs. 1-4; pl. 4, figs. 1-4; pi. 5, figs. 1-3; pl. 6, fig. 3; 



pi. 7, fig. I.) 



Cephalo-thorax. — Body elongate, with a thin epidermal skeleton 

 or crust. Cephalo-thorax small, short and broad ; in an entire dorsal 

 shield having a length of 123 mm., the cephalo-thorax has a length 

 of 15 mm. and a width of 56 mm.; surface depressed convex, as 

 flattened in the shale ; outline broadly rounded and almost trans- 

 verse across the front, rounding gently at the antero-lateral angles 

 before arching backward to the eye lobe where it curves slightly 

 inward. The eye forms a distinct lobe a little more than one-third 

 the length of the cephalo-thorax ; it is situated close to the postero- 

 lateral angle and has a narrow rim caused by a slight intermarginal 

 depression. The posterior margin is transverse and without any 

 intermarginal furrow. No traces of ocelli have been observed. 



A very large transverse epistoma is attached to the ventral edge 

 of the cephalo-thorax; in one example (pl. 5, fig. 3) it is nearly as 

 wide as the cephalo-thorax and apparently quite as long, if not 

 longer; the surface is smooth except for a slight intermarginal 

 furrow which is indicated at the sides and posterior margin; the 

 posterior outline is nearly transverse in the central portions and 

 broadly curved at the sides ; a large specimen having a width at 

 the third abdominal segment of 87 mm. and a length of 143 mm. 

 exclusive of the cephalo-thorax, has an epistoma 2y mm. in length 

 and over 55 mm. in width. The ventral appendages of the cephalo- 

 thorax will be described under the sub-heading Appendages. 



Abdomen.— The abdomen has twelve segments as shown by fig. i, 

 pl. 2 and fig. 2, pl. 5. The anterior nine segments form a broad 

 ellipse, the anterior end of which is attached to and merges into the 

 outline of the cephalo-thorax ; the length of these segments is about 

 one-eighth of their width ; the first segment terminates in a point 

 equally converging from the front and back margins ; in the second 

 segment the convergence and curvature is greatest toward the front 

 side and back of this the curvature of the front margin increases 

 until there is a slight backward arching of the posterior margin so 

 as to form a sharp point with the downward arching front margin ; 

 posteriorly the tenth and eleventh segments are nearly as long as 

 wide, much narrower than the first nine segments and more than 

 twice as long as the anterior segments from which they extend 

 backward ; they appear to be simple, annular rings ; the twelfth or 

 terminal segment has a central body, broadly oval in outline, that 



