134 BRITISH PALEOZOIC PHYLLOCARIDA. 



appendages as supplying a distinctive character in the different species, we find 

 that — 



The Style and Stylets are of equal or nearly equal length in — 



Length of Length of 



Carapace. Stylets. 



mm. mm. 



,.., . ~ , . ■■■ i a a ( 85 and 30 and 



Dithyrocaris Uolei, xxni, 1 — * ; xxiv, 4 s qcc ._ 



— testudinea, xxiv, 7 37 ... 11 



— Neilsoni, xxix, 3 a, b, e ? ... 26 



— (Bhachura) venosa, xxix, 4 ? ... 48 



— carbonaria, xxix, 5, 6 ? ... 22 



— Kochi, xxix, 7, 8 ? ... 25 



— breviaculeata, xxix, 9 ? ... 15 



The Stylets are shorter than the Style in — 



Dithyrocaris testudinea ? xxiii, 7 27 ... 9 



— Scouleri, xxv, 6 37 ... 25 



— Kayseri ? 50 



The Stylets are rather longer than the Style in — 



Dithyrocaris Dunnii, xxiii, 9, 10 ; xxix, 1, 2 ? ... 11? 



f 3° 23 



— glabra, xix, 3 ; xxni, 11 \ ^7. , r 



— testudinea, xxi, 4 47 ... 14 



and longer in — 



c 9 ^(* 



Dithyrocaris lateralis, xxiii, 5,6 i p , 9 



— testudinea, xxi, 5 ; xxiii, 8 ; xxxi, 4 ? ... 14 



— tricornis, xxiv, 6 80 ... 33 



— insiqnis, xxx, 1— 3 ; xxxi, 6 ( 43 arid | gQ ? 



( 50 ) 



Mesothyra ocean i 140 ... 70 



and much longer in — 



Mesothyra Neptuni ? ... 110 



The measurements are so often difficult to make and unsatisfactory, on 

 account of the frequent imperfections in the specimens, that the results obtained 

 do not supply us with definite characteristics for the species at present catalogued. 

 Besides the obscurity and breakage of parts there are several reasons for the 

 apparent variations in the relative length of the caudal spines, both one with 

 another and with the size of the carapace. Stages of growth, sexual difference, 

 and the systematic variation of feature and character have to be taken into con- 

 sideration, and the material at our command has not yet enabled us to arrive 

 always at definite conclusions. 



The carapaces and their halves are all here figured with the front end 

 upwards and the posterior downwards. The straight edge (dorsal or upper) of 



