Willemoesia Group of Crustacea. 281 



directed tooth. Anterior pair of pereiopoda having the outer 

 margin of the meros smooth, and the inner fringed with small 

 spines, and a large anteriorly directed tooth on the inner sur- 

 face of the dactjloid process of the propodos. Picon cari- 

 nated, the five anterior somites produced into sharp, anteriorly 

 pointed cusps. 



Taken in lat. 21° 38^ N., long. 44° 39' W., at a depth of 

 1900 fathoms, in the middle of the North -Atlantic Ocean, on 

 a bottom of Glohigerina-oozQj with a bottom-temperature of 1°'9 

 C, and near the island of Juan FernandeZj at a depth of 1375 

 fathoms on Glohigerina-oozQ, 1°'8 C. 



PoLYCHELES, fathoms. Temp, 



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



HeUeri Kermadec Isl. 520 6° Hard. 



„ New Guinea. 1070 2°-l Glob.-ooze. 



baccatus Fiji. 310 .. r.c. 



typlilopa Mediterranean. 



Pentacheles. 



Isevis Philippine Isl. 500 5°'3 Glob.-ooze. 



Suhmi Patagonia. 120 . . Mud. 



gracilis Fiji. 610 3°7 Glob.-ooze. 



obscurus New Guinea. 1070 2°-l Glob.-ooze. 



auriculatus Fiji. 610 , . Glob.-ooze. 



enthrix New Hebrides. 315 . , r.c. 



Willemoesia. 



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



„ Juan Fernandez. 1375 1°'8 Glob.-ooze. 



The eyes of the several genera although they may differ 

 from each other in structural detail, yet correspond through- 

 out 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 pre- 

 viously 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 tlie same way as the zoea 

 of Aljjheus in the embryonic condition has eyes consi- 

 derably larger and more like the permanent organ in other 

 genera than the adult parent from which it springs. 



The alteration from the original type to a depauperized 

 condition is therefore due to a cause acting through the habits 

 of the animal after it has passed through its zoea stage. 

 This is precisely the way that Alpkeus has passed; and as 

 the result has been somewhat similar, it is highly probable 

 that the conditions have been parallel. 



