1880.] NATURAL SCIENCES OF PHILADELPHTA. 53 



without armature. The tongue with transverse thickenings of the 

 rhacliis ; the lateral plates somewhat depressed ; the two first different 

 from the rest, larger and with a denticle at the root of the hook ; the rest 

 without any such, the external quite without a liook. A sucking-crop 

 on the upper side of the bulbus pharyngeus, but sessile, depressed con- 

 ical, and not consisting of two symmetrical halves. The large 

 stomach free on the surface of the liver. The glans of the long 

 penis with a strong and quite peculiar armature, consisting of strong 

 hooks, partly simple, partly bifurcate and partly digitate, with strong 

 digitations. The vagina with a peculiar armature of high palisades. 



This interesting genus externally most resembles the LameUidorides, 

 both in reference to the nature of the back, to the form and size 

 of the gill and in the want of armature of the lip-disk ; the region of 

 the openings of the rhinophor-holes differ in the want of a glabella 

 and by the presence of a larger number of surrounding papilte. The 

 genital opening somewhat recalls the Acanthodorides, as do also the 

 (tripinnate) branchial leaves and the sucking-crop, but this is not 

 divided in two distinct halves as in this last genus. The armature 

 of the tongue is very different from that of the LamelUdorides, 

 Adalarise and Acanthodorides ; the large hook-formed lateral plates 

 of these genera are wanting, and in their places are two large de- 

 pressed lateral plates, with small hooks ; the external plates somewhat 

 recalling those of the Adalarise ; the rhachis rather broad, with 

 transverse thickenings of the cuticula, corresponding to the rows of 

 plates. In the very peculiar form of armature of the glans penis, and 

 by the peculiar clothing of the vagina, the Akiodorides differ from all 

 the above-cited genera. 



Only a single species of the genus is hitherto known, the new one, 

 that wnll be described below. 



1. Ak. lulescens, Bgli., n. sp. Oceanum Pacificum. 



1. Ak. lutescens, Bgh., n. sp. PI. IV, fig. 3; pi. V, fig. 11-U: pi. VI, fig. 1-20; 

 pi. VII, fig. 1-8; pi. VIII, fig. 1-2. 



Color lutescens. 



Habitat. Oceanum Pacificum septentrion. (Nazan Bay). 



Of this form I have had a large single specimen for examination, 

 obtained in August, 1873, by Dall, on stony bottom, at low water, in 

 Nazan Bay, Atka Island, Aleutians. 



According to Dal), the color of the living animal was "yellowish- 

 white;" preserved in spirits, it was of a uniform dirty yellowish color. 



