Ortmann — Linujparus atavus. 291 



four different families. • Only Palinurus and Palinustus on the 

 one hand, and on the other Panulirus and Puerulus are more 

 closely related to each other: the other genera differ so widely 

 that they indicate as many lines of development within this 

 family, which are separated since very old geological times. 

 It may be possible to trace back the separation of these lines 

 of development into the earlier Jurassic or even into the 

 Triassic period. 



There are three chief groups, namely : 1, that of Palinu- 

 relhis and Jasus / 2, that of Palinurus, Palinustus and Lin- 

 uparus j 3, that of Panulirus and Puerulus. 



According to the morphological characters the first may be 

 called the more primitive, the second the typical, the third the 

 more advanced group. But perhaps it would be well to place 

 Palinurellus and Jasus in separate groups, since both — 

 although agreeing in some characters not found in the other 

 genera — are so widely different, that no closer genetic relation 

 seems to be present. 



The most striking character of Palimiridce is the connec- 

 tion of the frontal parts of the carapace with the so-called 

 segment of the antennulse as well as with the epistoma, and, 

 on the other hand, the fusion of the basal points óf the stalk 

 of the antennae with the epistoma. The frontal part of the 

 carapace is always united with the segment of the antennulae 

 outside of the eyes, on either side, but in the two genera first 

 named there is a median connection besides : the rostrum is 

 bent downward and covers completely or partially the bases of 

 the eyes, thus reaching and joining the segment of the anten- 

 nulee. These two genera — Palinurellus and Jasus — are further 

 characterized by the lack of a stridulating apparatus, formed 

 by the first free joints of the antennas rubbing against the seg- 

 ment of the antennulee, which seems to be present in all the 

 other genera. 



The second and third groups are more closely related to each 

 other, but they are distinguished by one important character : 

 in the second the epistoma is divided longitudinally Jby a deep 

 furrow, which no doubt indicates the former separation of the 

 basal joints of the antennse fused into the epistoma. ^ This 

 furrow is wholly wanting in the third group, the epistoma 

 being smooth and even medially. The disappearance of this 

 indication of the primitive separation of the basal joints of the 

 antennse stamps the third group as a more advanced one than 

 the second. Besides, there is another difference : in the second 

 group the flagella of the antennulee are always short, while in 

 -the third group they are very much longer. 



Examining our fossil form, we see at once that it belongs to 

 the second group. The larger specimen shows plainly the con- 

 nection of the carapace with the epistoma and with the seg- 

 ment of the antennulee, outside of the bases of the eyes, while 



