10 PEOCEEDINGS OF THE JSTATIOiN^AL MUSEUM vol. 78 



pedigerous part of the body is reduced in Opahinia. In living 

 Anostraca the furca is absent only in the extreme form of Artemia 

 salina var hoppeniaym (S. Fischer) and in the very specialized genus 

 Thamnocephalus . 



5. The form of the frontal process, though comparable in general 

 v^ith that of certain modern genera has a much longer unpaired 

 proximal region and a correspondingly shorter distal paired portion. 



All of these differences with the doubtful exception of the num- 

 ber and nature of the foliaceous appendages point to Opahinia be- 

 ing considerably less generalised than the modern Anostraca. 



Other fossil Anostraca. — Fossil Anostraca are exceedingly rare. 

 Apart from the Burgess Shale forms only three species appear to be 

 recorded. The Eocene Artemia vecten-sis (H. Woodward)^ shows us 

 a species essentially like modern forms at the beginning of the Ter- 

 tiary. Apart from this form no member of the group is known be- 

 tween Palaeozoic and modern times. Two species are recorded from 

 the Coal Measures of Europe. Branchipusites anthrac'mus Golden- 

 berg (1875) from Saarbriicken is so fragmentary, being based on the 

 middle portion of a body with supposed foliaceous appendages, that 

 its Anostracan nature is open to doubt. Rochdalia parkeri H. Wood- 

 ward (1913) based on a whole individual from the Middle Coal 

 Measures of Sparth Bottoms, Rochdale, Lancashire, is fairly well 

 preserved and of great interest in the present discussion. The 

 specimen was fossilised in a small clay iron stone nodule. It is 28 

 mm. long and consists of a head, 11 pedigerous segments that are 

 clearly defined, and a " telson " with a '' lateral plate." The head 

 apparently bears a pedunculate eye; on its ventral surface lies a 

 structure which Woodward terms the " proboscis " and which pre- 

 sumably represents an unmodified antenna. In Woodward's fig- 

 ure very definite indications of a segment bearing an appendage lies 

 between the head and the first of his segments, so it is possible that 

 there are really 12 pedigerous segments. The appendages are fig- 

 ured as of the simplest foliaceous type, traces of the attachment of 

 branchiae are said to exist. The misnamed " telson " probably rep- 

 resents the last pedigerous segment bearing a laterally placed ap- 

 pendage which Woodward terms the " lateral plate " ; possibly one 

 or more post-pedigerous segments have become fused into this seg- 

 ment. The general appearance suggests strongly that considerable 

 reduction has occurred in the segmentation. In so far as Rochdalia 

 can be elucidated it is clearly closer to Opahinia than to any living 



1 This species was described by Woodward (1879) as Branchipodites vectensis. Daday 

 (1910) has with good reason referred it to Artemia, but it seems highly improbabli; that 

 the modern species salina is identical with the Eocene representative of the genus so that 

 Woodward's specific name should stand until the two species are conclusively proved to 

 be identical. 



