1492 THE VOYAGE OF H.M.S. CHALLENGER. 



Genus Thyropus, Dana, 1852. 



1852. Thyropus, Dana, Araer. Journ. Sci. and Arts, ser. 2, vol. xiv. No. 41. 



1852. „ Dana, U.S. Explor. Exped., vol. xiii. pt. ii. pp. 1008, 1012, 1443. 



1879. Tanyscelus, Claus, Die Gattungen und Arten der Platysceliden, p. 17. 



1886. „ Gerstaecker, Bronn's Klassen und Ordnungen, Bd. v. Abth. ii. p. 483. 



1887. Tliyropus, Bovallius, Systematical List of Ainph. Hyper., Biliang till K. Svensk. Vetensk.- 



Akad. Handl., Bd. 11, No. 16, p. 43. 

 1887. Tanyscelus, Claus, Die Platysceliden, pp. 43, 45. 



For the original definition of Thyropus, see Notes on Dana, 1852 (pp. 259, 269). 

 For Claus' shorter definition of Tanyscelus, see Note on Claus, 1879 (p. 492). His 

 longer definition is to the following effect : — 



" Body broad and produced, ventrally flattened. Point of the head outdrawn. 

 Maxillipeds broad. Terminal joint of the lower male antennae scarcely half as long as 

 the preceding joint. Mouth-organs projecting beak-like. Mandibles strongly elongated, 

 with narrow cutting-edge. MaxUlse with four comb-like dental-processes at the distal 

 end of the plate. The two pairs of gnathopods simple, only distinguished from the 

 following limbs by a shorter and more compact form. Laminar first joint of the fourth 

 peraeopods strikingly elongated and distally narrowed, with short pocket-shaped groove 

 at a distance from the ridge of the hind margin. Fifth pereeopods 1 almost completely 

 developed, with the laminar first joint long." 



Claus himself suggests that his Tanyscelus sphseroma may be the same as Dana's 

 Tliyropus diaphanus, and Bovallius without uniting the two species assigns them both 

 to the genus Thyropus. Judging by the figures and description which Dana gives of his 

 type-species, Tliyropus diaphanus, and especially by what he says of the eyes and 

 antennae, there seems good reason for accepting his genus, though the type species has 

 not yet been identified, and perhaps from defects or deficiencies in the account never will 

 be. Dana considered that Typhis ferus, Milne-Edwards, belonged to this genus, and 

 Spence Bate, as Claus has pointed out, wrongly made Thyropus diaphanus, Dana, a 

 synonym of Milne-Edwards' species under the name Thyropus ferus. 



Thyropus danse, n. sp. 



For the general appearance of the species Claus' figure of " Tanyscelus sphseroma " 

 may be consulted. The head is much deeper than long, with flattened front, a little 

 produced downwards ; the first two segments of the perseon very short, the fifth, sixth, 

 and seventh long, with conspicuously overlapping margins. 



Eyes not quite reaching to the front of the head, but leaving free the produced 

 lower point of it, and a long triangular space above t this ; the upper and lower groups 



1 In regard to the fourth and fifth perreopods, see remarks on the definition of the next genus, Parascdus. 



