PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 385 



broad, vertical iiotdi. Keproductive organs large and i)rominent ; the 

 two orifices are situated on a large tubercle in front of the gill. The 

 male organ, iu extension, is loug, slender, usnally curled, truncate, about 

 equal in length to half the breadth of the body; it is a tubular organ, 

 with a slit along the lower side, formed by the rolling np of a long, thin, 

 membranous process. At the posterior edge of the tubercle there is a 

 shoiter, tlat-pointed process, connected witli the female organs. Color 

 of dorsal surface yellowish brown, lighter or darkei', and reticulated 

 with dark brown, often si)ecked with flake white; gill and proboscis 

 dark purplish brown ; the proboscis w^ith a darker dorsal patch ; tenta- 

 cles sometimes crossed by dark brown bands. Foot salmon-color. 

 O(lonto])hore very large and broad, with 150 to 170 rows of teeth; no 

 median teeth ; all the teeth are similar in structure, and show only a 

 gradual change in form and size from the inner to the outer ones. The 

 inner ones are elongated, slightly curved, narrow-lanceolate, with a very 

 acute point and with a smaller, narrow, sharp denticle on the inner 

 edge, parallel to but shorter than the main point ; the outer teeth grad- 

 ually become shorter, blunter, with a smaller denticle, which fiimlly 

 nearly disappears. Length, usually 30""" to 40'"'"; breadth, 10""'^ to 14""". 

 About 20 miles south of Block Island (stations 814 to 817), in 38 

 fathoms ; about 70 to 74 miles south of Martha's Vineyard (stations 805 

 to 872), in Go to 192 fathoms, tine, compact sand, very abundant (140 

 specimens). Also 90 to 100 miles south of Newi)ort, 1'. I., in So to 225 

 fathoms (stations 873 to 879). Closely resembles Pleurobranchcea Novce- 

 Zealandiw in form and color. The latter is a littoral species. 



Derdronotus elegans Vcniil, sp. iiov. 



Form and general api)earance nearly as in D. arhoresccns, but rather 

 more slender. Branchia; with rather longer stems and less numerous 

 branches than in the latter, but similarly arranged. Tentacle sheaths 

 with the terminal lobes not so finely divided, and with a smaller branch 

 on the outer side, near the base. Frontal processes of the head numer- 

 ous, large, with elongated stems, and not so much branched as in D. 

 arhorcscens. Color everywhere nearly uniform pale salmon ; tentacles 

 more yellowish. The dentition is peculiar and distinguishes it easily 

 from both our other species. Median tooth stout, smooth, entirely desti- 

 tute of lateral denticles ; its free portion, in a dorsal view, is broad-trian- 

 gular, almost as broad as long, acute at tip; base transversely elliptical, 

 a little broader than the free portion. Lateral teeth about ten on each 

 side, slender, the outer two or three shorter, blunt or subacute; the 

 others are successi\ely longer and larger, and each has a more acute and 

 more oblicpie tip than those that precede it, except the inner one, wliich 

 has a shorter tip, with longer spinules. These lateral teeth are rather 

 suddenly curved inward where they begin to taper, and beyond the curve 

 the tip becomes nearly straight again, and very acute, while the anterior 

 edge of the curvature is covered with slender, sharp spinules. 



Proc. Nat. Mus. 80 25 Dec. 2S, 1^80. 



