Dr. Henry Woochcard — Note on Cyclus Johnsoni. 491 



Bearing in mind i\in,i Prestwichia rotundatn, P. Birtwelli, and other 

 Coal-measure forms of Xiphosura, apparently, are not more advanced 

 in development, as compared with the living king-crab, than the later 

 larval stages of Limidus polyphemiis when first quitting the egg, as 

 represented in our monograph above quoted, then, if we venture 

 to assume that the curious forms referred to the genus Cyclus are 

 but the larval stages of those Coal-measure Limuli, we may most 

 certainly conclude that they would represent in point of structure 

 the still earlier phases of Limulus, they having been, so to say, more 

 precocious in quitting the egg than their modern representatives. 

 For example, in the earlier stages of development of the fertilised 

 egg in Limidus polyphemus (pi. xxxiii, figs. 1 and 2, op. cit.) only 



a . 



X 2 



Cyclus Johnsoni, H. "Woodw., 1894. 

 Impression and counterpart of a specimen from the ' Pennystone ' Ironstone band of 

 the Coal-measures, Coseley, near Dudley. Dra^mi twice nat. size, a, a, antenna^ ^ 

 b, endopodite (?) of one of mouth-organs ; c, c, appendages of the posterior 

 segment of the body. (Original specimen in Bii'miagham University Museum.) 



seven or eight pairs of simple limbs are seen, corresponding willi 

 a similar number of cephalic somites, partially united dorsally, 

 the thoracico-abdominal segments and the short telson not behig 

 developed until a much later stage. 



This early or premature hatching out of the young characterises 

 the Phyllopoda, and indeed most living Entomostraca. In those 

 Trilobites whose early history is known the young, as in Sao, 

 Ptychoparia, TriartTirus, Proetiis, Acidaspis, and Dahnanites, ar& 

 almost as simple, or even more so, in their earliest known stages 

 as Cyclus (see Beecher and Barrande's figures infra, p. 492). 



It must, of course, be borne in mind that this is only a suggestion, 

 and may hereafter prove to be of no value ; still, the fact remains 

 that the first considerable development of Limidiis-Wke Crustaceans 

 occurs in the Coal-measures, only one small form, Neolimidus, being 

 met with earlier in the Upper Silurian of Lesmahagow. We may 

 also justly assume that Limidi may be found in all those deposits 

 younger than the Coal-measures, seeing that king-crabs are living 

 at the present day widely distributed on the east coast of North 



