218 



Dr. J. Gwyn Jeffreys on the 



[June 15^ 



The fii'st species {Tacliytrypane Jeffrey si) comes from station No. 9, at a 

 depth of 1750 fathoms. The body is elongate, being upwards of two inches 

 in spirit, and about one tenth of an inch in breadth, rounded in front, but 

 marked by the usual ventral ridges throughout the rest of its extent. 

 There are about thirty segments besides the head and tail, the anterior 

 being short, those in the middle very long. The head forms a short 

 cone, with a minute fiKform process at the tip. Xo bristles are visible 

 under a lens, the body being smooth and ii-idescent, like that of Linotry- 

 pane apogon, for the fine transverse lines are not conspicuous. Very 

 minute simple bristles are, however, present : there are no cirri. The 

 caudal process is separated by a well-marked furrow from the rest of 

 the body, and terminates in a slender recurved process bent do\^Tiward 

 and forward. 



In the structure of the body-wall Tachytrypane Jeffreysi forms an 

 uitermediate link between Linotrypane^ and the other forms connecting 

 both with Ammotrypane and Ophelia. The cuticle is greatly thickened 

 (as in Linotrypane)^ and a special process passes inward from the median 

 line on the ventral surface towards the nerve-cord. From each side of 

 the latter the oblique muscle slants to the body-wall, cutting off a seg- 

 ment of the longitudinal muscular layer ; but the projection of the sepa- 

 rated region is much less than in the Connemara specimen figured in the 

 Ann. & Mag. ISTat. Hist. 1875, x^ i. p. 369, and therefore more closely alhed 

 to the condition in Linotrypane. In the latter the slender oblique muscle 

 passes on each side from the ventral raphe upward and outward to the 

 body-wall, and the band causes no separation of the comparatively large 

 segment included between it and the ventral raphe. The oblique muscle 

 is much shorter and more powerful in Tacliy try pane, and the condition 

 leads to that in alhed forms which more nearly approach Ammotrypane. 

 In the latter the change is much greater, for a single deep narrow muscle 

 (apparently representmg the coalesced oblique muscles) occurs at the 

 ventral border, with the nerve-cord beneath ; and the two segments, 

 which in Tachytrypane only bulge to a slight degree, are here separated 

 from the body by the whole breadth of the deep transverse muscle just 

 mentioned, so that in cross-section each forms a prominent pear- 

 shaped lobe attached by a narrow pedicle. A further differentiation is 

 apparent in Op)helia ; for the great transverse ventral muscle splits, and 

 a division passes into the ventral pedicle on each side, while the nerve- 

 cord occupies the m*edian line superiorly. 



The other species, Tachytrypane arctica, is minute, more slender than 

 a young Ammotrypane aulogaster of the same length, and is devoid of 

 cirri, but the bristles are prominent and curve backward. The cephalic 

 lobe is less pointed, a pigment-speck exists on each side at the base, and 

 the form of the caudal process is characteristic, being funnel-shaped and 

 terminating in a smooth rim. The cuticle is dense, though less developed 

 * Proc. Eoy. Sue. Ediiib. vol. viii. p. 386 (1873-74). 



