292 Ortmann — Linuparus atavus. 



no median connection is present. The epistoma shows the 

 median longitudinal groove characteristic of the second group. 

 The flagella of the antennulse, however, are not preserved. 



There are three genera in the second group. The first is 

 the type genus of the family, Palinurus (containing two liv- 

 ing species); the others are Palinustus and Linuparus (con- 

 taining only one species each). Palinustus was proposed by 

 A. Milne-Edwards* for a deep-sea form from the West Indies. 

 The description of it is very poor and even incorrect in some 

 respects, and no figure of it has been published. I am, how- 

 ever, enabled — through the kindness of Professor Alexander 

 Agassiz, who lent me the type specimen for examination — to 

 state, that Palinustus comes very near to Palinurus, and differs 

 only in the weaker " frontal horns," which are placed on the 

 outer edge of two very peculiar plates projecting horizontally 

 from the frontal margin and truncated squarely at the apex. 

 In Palinurus these projecting frontal plates are wanting and 

 the "frontal horns" are formed by two large, compressed, 

 nearly falciform spines placed close to the frontal margin on 

 either side of the rostrum. In all other respects Palinurus 

 differs only slightly from Palinustus. The differences of both 

 genera from Linuparus are the following. In Palinurus and 

 Palinustus the carapace, especially the part behind the cervical 

 groove, is evenly arched from side to side, i. e. of sub-cylindri- 

 cal shape, and it is covered by a multitude of spines and spiny 

 tubercles, becoming scaly in the hinder part. The frontal 

 horns are compressed and separated by a wide space. In 

 Linuparus the hinder part of the carapace is distinctly cari- 

 nate, three keels being present, a median one and two lateral 

 ones. The surface is covered with granules, and a few small 

 spines placed chiefly on the anterior part, thus differing strik- 

 ingly from the spiny appearance of the carapace of the first 

 two genera, and, further, the frontal horns of the living Linu- 

 parus lie close together and are depressed (not compressed), 

 forming two broadly triangular plates projecting from the 

 middle of the frontal margin. 



Our fossil form comes very near to Linuparus in the shape 

 and armature of the carapace. There are three distinct longi- 

 tudinal keels on the hinder part of the carapace, and only a 

 few short spines distributed in a similar manner as in the living 

 Japanese form. But there is a difference in the frontal horns. 

 The latter are compressed, as in Palinurus, but nearer to the 

 median line. The horns are smaller than in Palinurus and a 

 little inclined, diverging from the bases outward, and thus they 

 are exactly intermediate in shape and position between the 

 living Palinurus and the living Linuparus: the distinct lateral 

 compression comes near to that of the former genus, but the 

 inclining direction looks like an incipient depression, and in 



* Bull. Mus. Compar. Zool., vol. viii, 1880, p. 66. 



