TRANSACTIONS OF SECTION D. DEPT. ZOOLOGY AND BOTANY. 563 



connection with the power of change in the form of the pereiopoda, that I purpose 

 classifying the several species of this interesting group. 



Polycheles, Heller. 



(Crust, des Bttdl. Eivropa.) 



In this genus I accept the author's definition, that it has the anterior four pairs 

 of pereiopoda chelate and the fifth simple. But instead of saying that the eyes 

 are rudimentary, I assert that they are immovably lodged in a notch in the dorsal 

 surface of the carapace, with the anterior extremity projecting heneath the antero- 

 lateral wings of the carapace. 



Pentacheles, n. g. 



All the pereiopoda are chelate, and the eyes are lodged immovahly in a notch 

 in the antero-dorsal surface of the carapace, with the anterior extremity projected 

 beneath the antero-lateral wing-like extremity of the carapace. 



Willemoesia, Grote. 



(* Nature,' October 1873.) 



All the pereiopoda chelate, and the ey r es immovahly situated in the anterior or 

 frontal surface of the cephalon, and neither lodged in a notch in the dorsal surface 

 of the carapace nor covered by the antero-lateral wing of the carapace. Eyes 

 small, directed outwards and forwards. 



Polycheles. 



Fathoms Temp. 



crucifer West Indies 450 . . . Glob.-ooze. 



Helleri Kermadec Island... 520 6° Hard. 



„ New Guinea 1070 2°-l Glob.-ooze. 



baccatus Fiji 310 ... r.c. 



typhlops Mediterranean 



Pentacheles. 



lsevis Philippine Islands 500 5 0, 3 Glob.-ooze. 



Suhmi Patagonia 120 ... Mud. 



gracilis Fiji 610 3°-7 Glob.-ooze. 



obscurus New Guinea 1070 2 0, 1 Glob.-ooze. 



auriculatus Fiji 610 ... Glob.-ooze. 



enthrix New Hebrides 315 ... r.c. 



WlLLEMOESIA. 



leptodactyla North Atlantic ... 1900 l°-9 Glob.-ooze. 



„ Juan Fernandez ... 1375 l° - 8 Glob.-ooze. 



The eyes of the several genera, although they may differ from each other in 

 structural detail, yet correspond throughout the group in a common characteristic. 

 The peduncle is reduced to a minimum and fixed as a rigid part of the dermal 

 structure, over which a portion of the carapace is projected. 



If we turn to the animal while it is yet embryonic (and our only opportunity 

 is its observation before it has quitted the egg), although in an advanced condition, 

 we see that previously to the eruption from the ovum it attains at least the zoea 

 stage of development, and that the eyes are large and distinctly pedunculated, just 

 in the same way as the zoea of Alpheus in the embryonic condition ha eyes con- 

 siderably larger and more like the permanent organ in other genera than the adull 

 parent from which it springs. 



The alteration from the original type to a depauperised condition is therefore 

 due to causes acting through the habits of the animal after it has pas <>d through 

 its zoea stage. This is precisely the way that Alpheus has passed; and as the 



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