160 GENUS HIPPA. [November. 



to the Brachyura is so imposing, that it is but recently it 

 has been referred to its true place in the system, yet it is 

 worthy of remark that the lateral processes are very con- 

 spicuous, crustaceous, and never withdrawn under the 

 middle division. In Monolepis, on the contrary, tlie 

 lamellae of the tail are minute membranaceous, hyaline^ 

 and entirely concealed beneath the middle division, to 

 which they are so closely applied that the unassisted eye 

 would not detect their presence. 



These differential characteristics, by which'^the genus 

 under consideration is distinguished, combined with the 

 form of the antennas, which it must be confessed is very 

 closely allied to that of the Brachyura, seem to indicate 

 its true situation in the system. It would indeed appear 

 to supply an intermediate shade, a more closely connecting 

 link in the gradation, by which the two orders to which I 

 have referred, are approximated. Hence in an arrange- 

 ment perfectly natural, it would be the first of the order, 

 but in the artificial system it will precede the genus Por- 

 cellana, forming of itself a division of the Macroura, 



Genus HIPPA. 



Hands simple, compressed and oval; the tarsus of the 

 second and third pairs of feet lunated, of the fourth trian- 

 gular. Eyes supported upon a filiform peduncle. 



SPECIES. 



1. H. talpoida.'^ Body convex, oval; four anterior 

 segments of the abdomen not inflected and having the 

 natatory appendices of the tail, reflected on their sides; tail 

 elongated, more than half as long as the body, sublanceolate; 

 clypeus with two sinuses forming three teethe eyesm\n\xX.Q» 



