386 



CHAS. CHILTON. 



and in general shape looks like a Ligia, but "its appearance 

 earlier than the primitive caridoid forms may, however, 

 justify some suspicion as to its affinities. Praearcturus 

 Woodward, from the Old Red Sandstone of Herefordshire, 

 has very slender claims to be admitted into this order, and 

 the same may be said of Amphipeltis Salter (Devonian of 

 Nova Scotia), and Arthropleura Jordan (Coal Measures)." 1 

 Undoubted Isopoda do, however, appear in Secondary Rocks. 

 Cyclosphceroma Woodward, from the Great Oolite and Pur- 

 beck and Archceoniscus Milne-Edwards from the English 

 Purbeck appear to belong to the Sphaeromidse, and if so, 

 would indicate that that family was differentiated as far 

 back as the Jurassic Period. Eosphasroma Woodward from 

 Eocene and Miocene also appears to belong to the same 

 family. Palcega Woodward and Proldotea Racovitza and 

 Sevastos, resembling the existing Mga and Mesidotea 

 respectively, are known from Oligocene beds. 



Urda Miinster from the Jurassic of Solenhofen appears 

 to resemble the male of Gnathia. 



The existence of Phreatolcus as a fossil in the Triassic 

 beds of Australia is therefore quite in harmony with the 

 little that is known of the fossil Isopoda and forms a most 

 important addition to their geological history. 



6. Analogy with the Anaspidacea. 



It is perhaps worth while calling attention to the fact 

 that in Tasmania species of Phreatoicus are found in the 

 same waters as the peculiar fresh- water shrimps Anaspides 

 tasmanice and Paranaspides lacustris. These shrimps 

 have been shown by Caiman (1896) to be nearly related to 

 Palceocaris, Prceanaspides, etc., from the Permo-carbon- 

 iferous of Europe and North America, the whole forming a 

 group which Caiman has named Syncarida. Another living 



1 Caiman, in ZitteFs Palaeontology, Second Edition, p. 75S. 



