GEOLOGICAL RECORD. 



mon Salter. Whether these are to be regarded as true Decapods 

 or as belonging to either of the groups of Schizopods is an open. 

 question, as is, indeed, the case with regard to some existing 

 species. Pygocephalus, from the Coal Measures, appears to be 

 a true Schizopod, belonging to the division of the order classed 

 with the Peracarida.* Clearly marked Macrura appear in the 

 Trias and are well represented in Jurassic rocks. The first 

 undoubted Anomura and Brachyura occur in Cretaceous strata, 

 though Palaeinachus has fair claims to represent the latter 

 suborder in the Jurassic period. 



Sculda (Jurassic) and Squilla (Cretaceous) give the first clear 

 evidence of the Stomatopods. 



Cyclosphaeroma from the Great Oolite is undoubtedly an 

 Isopod, but it is far from certain that we possess any earlier 

 representatives of the order. It is interesting to recognize the 

 characteristic tumours caused by parasitic (Bopyroid ?) Isopods 

 in the fossil crabs (Palaeocorystes) of the Cambridge Greensand. 



The first unquestionable Amphipod is not met with until 

 the Tertiary (Miocene) strata, though a number of obscure 

 Palaeozoic forms have been referred to this order. No fossil 

 Cumacea have been recognized. f 



On reviewing the palaeontological history of the several orders 

 of Crustacea, the Entomostraca appear to have been differenti- 

 ated at a period before the record begins, and four of their five 

 orders were well established together with certain main types 

 of the Malacostraca (Leptostraca, Syncarida and the Caridoid 

 type) by the Carboniferous period. It may however fairly be 

 claimed that the order of appearance of the subdivisions of the 

 Malacostraca is consistent with the conclusions as to their 

 relationship to which we are led on purely morphological grounds. 



Sub-class 1. ENTOMOSTRACA. 



The name Entomostraca, though established by long usage, 

 is without etymological significance as contrasted with that of 



* Cf. H. Woodward on the genus Pygocephalus Huxley, a primitive 

 Schizopod Crustacean, from the Coal Measures. Geol. Magazine, decade 

 5, vol. iv, p. 339, Sept. 1907. 



f The author desires to express his indebtedness to Mr. H. Woods of 

 St. John's College, Cambridge, for his assistance in preparing this notice 

 of the palaeontological record of the Crustacea. 



