1909.] NATURAL SCIENCES OF PHILADELPHIA. 273 



Pista (Scionopsis) alata sp. nor. (Plate IX, figs. 48-51). 



Form moderately stout, widest and somewhat depressed anteriorly, 

 tapered regularly to caudal end. Length of type 63 mm., maximum 

 width at X 9 mm. Number of segments 94, in addition to a few 

 scarcely differentiated ones at the caudal end. 



Prostomium rather small but prominent, thickened, arched, its 

 sides continued ventrad to nearly enclose the mouth, below which 

 they end in a pair of short, thick lobes each bounded laterally by a 

 slight indentation. Tentaculiferous ridge low and thick, bearing- 

 numerous tentacles arranged in a single transverse row in the medial 

 and in two transverse rows in the lateral part. Tentacles numerous, 

 rather short and thick, very slightly attached by a contracted base 

 and deeply grooved or folded for most of their length. Many of the 

 dorsalmost ones are short and imperfectly developed. 



Peristomium and two or three immediately following segments 

 short, contracted and terete. Peristomium produced into a promi- 

 nent ventral fold with a deep median emargination, on each side of 

 which it spreads laterally as a great flaring wing reaching dorsally to 

 the level of the setigerous tubercles. Somites II and III are distinct 

 dorsally and ventrally but confounded laterally. The anterior margin 

 of the former is produced on the ventral surface as a slight fold. 

 Beginning at the sides of the ventral plate of III is a pair of conspicuous 

 wings which extend obliquely up the sides of III and the anterior 

 margin of IV and which are united across the dorsum of the latter by a 

 transverse fold bearing a prominent median forward projection. 



Posterior to the branchial region the thoracic segments develop 

 prominent glandular thickenings along the parapodial field, as a result 

 of which they are wider than deep. Behind X the thoracic region 

 tapers into the abdomen, the transition into which is somewhat abrupt. 

 Ambulation of the somites is obscure, only the posterior thoracic and 

 anterior abdominal showing faint indications of subdivisions. There 

 are fourteen well-marked ventral plates, the first on III, the last on 

 XVI, behind which more obscure wrinkled and subdivided areas 

 continue to the end of the thorax. The first five are short, about 

 four or five times as wide as long. The others are very smooth, 

 apparently very vascular and probably deep red in life, the relative 

 width gradually increasing from equality to the length to double it, 

 the greatest width in all cases being anterior, so that the entire series 

 appears serrated laterally. By the sides of each is a pair of rough 

 glandular areas which posterior to XVI become united with the gland- 

 ular ventral areas, giving them an irregular polygonal outline and 

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