596 THE VOYAGE OF H.M.S. CHALLENGEE. 



seven-articulate. The third, fourth, and fifth pairs are subequal in length, and resemble 

 each other in form, they are moderately robust and terminate in a dactylos that is 

 serrate on the inner margin and terminates in a double unguis. 



The posterior pair of pleopoda is subequal in leugth with the telson, the outer ramus 

 being furnished with a diaeresis that is armed with a tooth at the outer margin, and the 

 telson is dorsally smooth and dorso -laterally furnished with short spines on each side, 

 and spines and hairs at the extremity. 



The preceding description is taken from Cancer spinas, Sowerby, which is 

 synonymous with Hippolyte sjrinus, Leach, and which the latter made the type of his 

 second division of Hippolyte. But since Leach's definition was chiefly based on the 

 variable feature of there being four instead of two spines on each side of the dorso-lateral 

 surface of the telson, its position in the genus with Hippolyte varians cannot be main- 

 tained in the face of more important structural differences. 



The branchiae consist of six pairs arranged as in the annexed table : — 



Pleurobranchiae, . . . 1 1 1 1 1 



Arthrobranchise, . . . 



Podobranchise, 

 Mastigobranchia?, 



Geographical Distribution. — North Atlantic Ocean and Arctic Seas. 



Spirontocaris spinus (Sowerby) (Pis. CVL, CVIL). 



Cancer spinus, Sowerby, Brit. Misc., 1806, pi. xxi. 



Alpheus sp>inus, Leach, Trans. Linn. Soc. Lond., vol. xi. p. 244 ; Edin. Encyclop. Sup., vol. 



vii. p. 421. 

 Hippolyte sowerbsei, Leacb, Malacos. Podophtli. Brit., pi. xxxix. figs. 1, 10. 



„ sowerbcei, Desmarest, Consid. sur les Crust., p. 223, pL xxxix. fig. 1. 

 „ sowerbyi, Milne-Edwards, Hist. Nat. Crust., torn. ii. p. 380. 

 Hippolyte spinus, Owen, Boss's Second Voyage for the Discovery of a North-West Passage, 

 Append., p. lxxxiii., pi. iii. fig. 2. 

 Bell, Brit. Stalk-eyed Crust., p. 284. 

 „ „ White, A., Pop. Hist. Brit. Crust., p. 118, pi. ix. fig. 1. 



„ seeurifrons, Norman, Brit. Assoc. Eep., 1861 ; Trans. Tyneside Field Club, p. 267, 

 pi. xii. figs. 1, 7, 1862. 

 Hippolyte spina, Stimpson, Proc. Acad. Nat. Sci. Philad., 1869, p. 106. 

 „ „ Kingsley, Proc. Acad. Nat. Sci. Philad., 1879, p. 418. 



Leach's definition is as follows : — " H. rostro alto obtuso supra multi-serrato apice 

 emarginato serrulato ; subtus unisonato." 



Carapace dorsally carinated and armed with five large teeth, commencing close to 

 the posterior margin. Eostrum armed with one or two large teeth and a serrature of 

 several minute ones, terminating more or less abruptly posterior to a sharp apical point ; 

 lower margin deep anteriorly and armed with two large teeth, and a serrature of several 



