948 The Palceosoic Allies of Nebalia. [December, 



published a brief notice of the leading characteristics of the 

 y^J group, and proposed that the 



p j M Palaeozoic fossil forms, Ceratio- 



f • / ft:.'. ^"^>^. Cari " S ' etC -' be UpitecJ Wltn the 



Vbuliacl.-u to form a separate 



order of Crustacea under the 



jj^^ name of Phyllocarida. 



jf,if %BKm ( ^ tne fossil forms, Hymeno- 



vflV can's was regarded by Salter as 



^^^ "the more generalized type." 



, The genera Peltocaris and Dis- 



wedge-shaped rostrum in situ. Ait^r cmocaris characterize the Lower 



Silurian period, Ceratiocaris the 



Upper, Dictyocaris the Upper Silurian and the lowest Devonian 



strata, Dictyocaris and Argus the Carboniferous period. 



On examining the figures of Salter and of Barrande, for we 

 have been unable to study any of the fossils themselves, owing 

 to their extreme rarity, the relationship to Nebalia is very 

 marked, as seen in the form of the carapace, the nearly free or 

 detached rostrum, unless the separation took place after the 

 death of the animal, and also of the rather long, slender abdomen. 

 Upon examining the appendages at the end of the abdomen there 

 is to be seen an important distinction from Nebalia; a long, slen- 

 der telson is usually present, with a single pair of large caudal 

 stylets, or cercopoda, in form like those of Nebalia. But in Hy- 

 menocaris and Peltocaris the telson appears to be represented by a 

 pair of small (in Peltocaris minute) spines. In the presence of the 

 telson in the typical fossil genus Ceratiocaris, we certainly have 

 an important character separating the type with its allies from 

 Nebalia, and allying them to the Decapods; and thus in the pro- 

 visional synopsis of the order presented in the memoir soon to be 

 published in Hayden's Report, we have placed the fossil forms in 

 a separate sub-order from the Nebaltadae. 



While the posterior edges of the abdominal segments in Hy- 

 menocaris appear to be spined as in Nebalia, there are some char- 

 acteristics of importance in the fossil forms which deserve men- 

 tion ; these are the sculptured carapace, especially of Dictyocaris, 

 in which the surface is reticulated. 1 Moreover the size of these 



structure is plainly seen in the pare, 

 ely too minute to be perceptible in the 



