92 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



could find of published data, and here exhibit the series in a dia- 

 grammatic form, that the naturalist may judge for himself whether 

 it bear out the view of Darwin, or no. 



I do not think, judging by the carapace only, that many links are 

 wanting between the Llandeilo-flag Veltocaris and the Upper Silu- 

 rian Ceratiocaris. But there is evidently a still nearer connexion 

 (probably we want an intermediate Devonian form) between Cera- 

 tiocaris and Dithyrocaris. The Argas of the Lower Carboniferous 

 rocks, and a huge bivalve Crustacean not here described*, were close 

 relations of the Dictyocaris and Ceratiocaris of the Upper Silurian, 

 differing only in having the anterior joints of the abdomen concealed, 

 and the rostrum minute or possibly (but not probably) absent. 



The links between these Coal-measure forms and those of recent 

 times are many of them wanting ; but in Nebalia we have a good 

 representative of the compact, shield-shaped form of Ceratiocaris, the 

 two valves soldered into one, and the rostrum attached, — the eyes 

 being still beneath the carapace. Apus is the most complete and 

 decided form, and it is one of the latest of this group, as it commences 

 in the Trias. The abdomen is not only greatly increased, and the 

 caudal styles elongated beyond the telson, but the styles are jointed 

 appendages; and the feet and antennae have also taken on a de- 

 velopment wholly beyond that of the rest of the order. 



The other group, the truly bivalved and enclosing Phyllopods, do 

 not present the same variety of forms. From the period of the 

 Middle Devonian, where Esiheria first makes its appearance, till 

 now, there has been but little change, except a gradual increase in 

 size. And, as I do not feel sure that we have in the EstJieria or 

 Leperditia the oldest member of the series, I will only place them 

 as they stand in the diagram, and abstain from discussing the affini- 

 ties of any but the larger and shield-bearing Phyllopods. 



I may be permitted to say, that even of these the series, as here 

 exhibited, is not quite satisfactory in a Darwinian point of view. 

 The transition, if it be such, from Hymenocaris, with an entire shield, 

 to a form with sutures, and then valves, returning afterwards to a 

 more completely soldered and compact form, may be regarded as an 

 oscillation of character by those who do not see a more embryonic 

 representative in the thin undivided carapace (without rostrum, 

 suture, or external eye) in the primordial form. Apus, however, is 

 unquestionably the most highly developed ; and it is the latest. 



On some Tracks of Lower Silurian Crustacea. By J. W. Salter, 

 Esq., F.G.S., A.L.S., of the Geological Survey of Great Britain. 



[Eead May 21, 1862.] 



This short communication seemed hardly worth the Society's 

 notice, and would have been long delayed, but for the appearance 

 of a most interesting photograph-plate in the ' Transactions of the 



* Dithyrocaris Pholadomya, MS., a species with a carapace 7 inches long, from 

 the Carboniferous Shales of Berwickshire. 



