1902.] AND ANCIENT GEOGRAPHY. 307 



of this subfamily, it is necessary to discuss the systematics of it. 

 Ortmann distinguishes four genera : Potamocarcinus, Epilobocera, 

 Hypolobocera and Kingsleya, while Rathbun accepts the following : 

 Epilobocera, Potamocarcinus, Pseudothelphusa and Rathbunia. 

 Generally, Ortmann's Potamocarcinus corresponds to the genera 

 Potamocarcimts and Pseudothelphusa of Rathbun, and the close 

 affinity of these two is also admitted by Rathbun, so that their 

 union (under Potamocarcinus) is well supported. But in this case, 

 we are to exclude from Potamocarcinus the species sinuatifrons 

 Kgsl. (and Ortm., nee A. M.-E.) = haytensis Rthb., which be- 

 longs to Epilobocera. If we add this latter species to Ortmann's 

 Epilobocera, this genus corresponds exactly to Epilobocera Rath- 

 bun. Hypolobocera of Ortmann is classed by Rathbun with Pseudo- 

 thelphusa {Potamocarcinus of Ortmann), and rightly so, as we now 

 believe. Kingsleya Ortmann is put by Rathbun with Potamocar- 

 cinus (sens, strict.); this, however, does not seem to be justified, 

 since then the very peculiar shape of the orbita is neglected. While 

 in all other forms of the subfamily the lower orbital margin pos- 

 sesses on the inner end a suborbital lobe, which may unite with the 

 front, in Kingsleya the lower orbital margin itself joins the front, 

 while the suborbital lobe is hidden. This character, connected 

 with the extremely reduced condition of the exopodite of the third 

 maxilliped, which also does not find its like in the whole subfamily, 

 fully warrant, in our opinion, the creation of a separate genus. The 

 genus Rathbunia of Nobili is founded upon a single species, and 

 its chief character is taken from the shape of the meropodite of the 

 third maxilliped, which is narrower than usual at the proximal end. 

 In all other respects this genus agrees absolutely with Pseudothel- 

 phusa (resp. Potamocarcinus of Ortmann), and a generic separation 

 does not seem to be necessary. 



As a compromise between both generic divisions I should like to 

 suggest the following: 



Genus: Epilobocera Stps. (corresponding fully to Epilobocera 

 Rathbun). 



Genus: Potamocarcinus M.-E. (= Potamocarcinus Ortm. (ex- 

 cluding sinuatifrons Ortm. = haytensis Rthb.) -f- Hypolobo- 

 cera Ortm.). 

 i. Subgen. Potamocarcinus M.-E. (genus, according to 

 Rathbun, excluding the species latifrons Rand.). 



