NO. 6 MIDDLE CAMBRIAN BRANCHIOPODA, ETC. 1/9 



leg when flattened so as to bring this feature in profile. These tri- 

 angular expansions also show on the fourth and fifth joints of some 

 specimens. One specimen shows on seven pairs of legs, small, elon- 

 gate, oval bodies attached near the first joint to the outer side of the 

 leg. These bodies left but slight impression on the rock and are 

 rarely seen. They appear to represent the gills. 



A pair of minute, jointed, setiferous appendages projecting from 

 beneath the first abdominal segment suggests the presence of a simple 

 phyllopodan natatory leg. The remaining thirty or more segments 

 of the abdomen an4 telson are limbless so far as can be determined 

 from many specimens. 



Interior structure. — The thin carapace has preserved and now 

 shows most beautifully the large hepatic caeca. The position and 

 connection of these is finely shown at (kd) by figures i and 2, plate 

 27. The alimentary canal is large, expanded in the head as a stomach 

 (st, fig. i), and extending directly through the body from the front 

 of the head to the first abdominal segment where it presumably termi- 

 nated at the anus. 



Dimensions. — The average length of the larger specimens of the 

 carapace is about 10 mm. Some are 12 mm. and many 6 to 8 mm. 

 The proportions of carapace, thorax, and abdomen are fairly well 

 shown by figure i, except that the long, thin abdomen continues back- 

 ward until it exceeds the entire length of head and thorax about 3 to 

 2, or by actual measurement in one example, 21 mm. to 12 mm. for 

 the head and body respectively. 



Observations. — The very delicate carapace resembles that of the 

 recent Lepidurus and like the latter takes many forms when flattened 

 by pressure. An illustration of the deformation of the carapace of 

 Burgessitt' is given by figures 3 and 4, plate 30. I at first thought 

 that the latter represented quite a different form from Burgessia 

 hella, but with the examination of many specimens a fine series was 

 selected, showing gradations between the typical specimens on plate 

 27, figures I and 2, and the crushed side views shown by figures 3 

 and 4, plate 30. I had selected many specimens to be photographed 

 but decided to illustrate only five in this preliminary paper as many 

 interesting points have come up that more material may throw light 

 on. 



Among living Branchiopoda the Apodidse furnish the most sug- 

 gestive examples for comparison with Burgessia bella. The absence 

 of abdominal segments with appendages is a marked distinction, also 

 the presence of eight pairs of thoracic legs. The long slender abdomi- 



