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



is straight and almost in a horizontal line with the dorsal surface of the carapace, rising 

 to the apex. The type specimen is armed with seven teeth, but the extreme tip of the 

 rostrum is broken off. Two others, not quite so large, have nine each, the apical one 

 being very small ; the last is above and behind the orbital margin of the carapace, and one 

 posteriorly remote upon the gastric region, whence the dorsal crest is continued with 

 but a minimum of elevation to the posterior margin of the carapace. Two longitudinal 

 ribs traverse the carapace in a slightly oblique direction, just above the branchial 

 region. The orbital tooth is very minute, while the antennal tooth is well formed and 

 prominent, as also is the tooth on the hepatic region. 



The pleon is marked with a median longitudinal carina that is visible on the dorsal 

 surface of the second somite, and gradually increases to a small ridge on the sixth 

 somite, where it ends abruptly and is not produced to a tooth. The sixth somite is 

 compressed laterally, and so to a less extent is the fifth. The telson is dorsally longi- 

 tudinally grooved, and the sides ribbed, smooth, and fringed with fine hairs, and the 

 extremity terminates in a sharp point. 



This species differs from the type specimens of Penseus affinis, preserved in the 

 Museum of the Jardin des Plantes, as described by Milne-Edwards, in having the rostrum 

 straight, instead of being curved upwards at the extremity. 



The notch on the meros of the fifth pair of pereiopoda is equally distinct, but that on 

 the rhipidura is less marked. There is a slight variation also in the folding of the 

 petasma. 



The females in the collection correspond with the males, except in the absence of 

 the peculiar excisions on the base of the fifth pair of pereiopoda, and on the outer plates of 

 the rhipidura. The female specimens are small and probably immature, being only 31 

 mm. in length. 



In the female the thelycum or ventral plate is shaped like the conventional figure of 

 a heart, with the apex directed anteriorly. 



The resemblance of this species to the type, Penseus affinis, is so great, that in spite of 

 the various differences, I have some hesitation in considering it anything more than a 

 modified form. 



Penseus anchoralis, n. sp. (PI. XXXV. fig. l). 



Surface tomentose. Eostrum dorsally horizontal, slightly elevated at the apex and 

 armed with eight small teeth, subequally distant, and one small one further separated 

 and situated on the gastric region. Lower margin smooth, gradually ascending in a 

 curved line to the apex. Frontal margin armed with a small supraorbital and an 

 antennal tooth, and one on the hepatic region. Third and succeeding somites of the pleon 

 carinated, the sixth terminating in a small tooth. Telson pointed, dorsally flattened and 



