607 



with the carpus exceedingly large and more or less produced below, so as to 

 form together with the propodos and dactylus a complex chela. Anterior 

 pairs of pereiopoda subequal, with the basal joint large and broad; the 3 

 posterior pairs comparatively short and strongly recurved, with the dactylus 

 small and inverted. Branchial lamellae narrow, and only present at the base 

 of the 3 middle pairs of legs. The 3 anterior pairs of incubatory lamellae 

 likewise narrow; 4th pair, however, large and expanded, closing the marsupial 

 pouch posteriorly. First pair of pleopoda rather large; the 2 succeeding pairs 

 imperfectly developed. Penultimate pair of uropoda uniramous; last pair 

 with the terminal joint extremely small, and hook-shaped. Telson short and 

 broad, slightly bilobed, upper face densely spinous. 



Remarks. The present genus was established by Say as early as in 

 the year 1817, to include a North American species, C. tulndaris. This species 

 has subsequently been described more in detail by Prof. S. J. Smith, and has 

 turned out to be very different from the species referred by European authors 

 to the genus Cerapus. On the other hand, a form referred by Sp. Bate to 

 the genus Siplionoecetes (S. crassicornis) and subsequently found off the Norwe- 

 gian coast, shows itself evidently to be congeneric with the above-named 

 North American form. The genus agrees with the other Corophiida as 

 regards its outward appearance, though, as above mentioned, exhibiting in 

 the anatomical details some points of resemblance to the genus Erichthmius. 

 Besides the typical form and the northern species described below, the Rev. 

 Mr. Stebbing has recorded 2 new species from the Challenger Expedition, as 

 C. SismitM and C. Flindersi. 



1. Cerapus crassicornis, (Sp. Bate). 



(PI. 217). 

 Siplionoecetes crassicornis, Sp. Bate, Catal. of Arnph. Brit. Mas. p. 269, PI. XLV, fig. 9. 



Body much depressed and rather slender, with the metasome and 

 urosome generally folded in beneath the posterior part of the mesosome. 

 The 2 anterior segments of mesosome in female much shorter than the succeed- 

 ing ones, in male considerably larger, especially the 2nd. Cephalon produced 

 in front to a rather large and acuminate, horizontally projecting rostrum, 

 lateral lobes short and obtusely rounded at the tip. Anterior pairs of coxal 

 plates extremely small; 5th pair much larger than the others, and having 

 the anterior lobe very broad and deep. Epimeral plates of metasome evenly 



