76 BRITISH PALEOZOIC PHYLLOCARIDA. 



harder covering ; yet Mr. Salter's determination of the more truncate or wider 

 (higher) end of the carapace being the hinder margin seems to be well founded, 

 whether the abdomen be still in apposition or not. 



The crumpled bed-planes of the hard shale or flagstone frequently exhibit 

 crushed body-joints of the Rymenoearis ,- but these relics of the abdominal 

 portion vary much in the number of attached segments. Sometimes four or five, 

 but not uncommonly six or seven body- joints occur, with or without the telson 

 being apparent. Bight or nine together are less frequent. In one instance (in 

 the Owens College Museum) ten or eleven segments can be counted, besides an 

 obscure telson, in an unattached body (PI. XIII, fig. 10) lying on a slab containing 

 numerous specimens of carapaces and body-rings of Hymenocaru (from Gareg- 

 felen, collected and given by Mr. D. Homfray). In this case some (five or six) 

 segments, which appear to have been softer than the others, may have been 

 within the carapace, for they differ from the others in size and distinctness of 

 outline. 



The crushing and squeeze have rendered even the best and most promising 

 specimens so obscure that much doubt still exists in the observations on this 

 Phyllopod. Mr. Salter determined nine exposed body-rings (' Mem. Geol. Surv.,' 

 vol. iii, p. 293, but only eight are shown in his pi. ii, fig. 4), with one pair of 

 styles and two pairs of stylets attached to the last joint (op. cit., pi. v, fig. 2). 

 The abdominal joints vary from about yo to ^ inch (7 to 9 mm.) in height, 

 sometimes to -^^ (12 mm.), very rarely to -^ and -^ (15 and 17| mm.), but in one 

 case to 1% inch (20 mm.), according to size of individuals and the accidental 

 crush. 



The caudal appendages consist of six setjB, springing from the terminal edge 

 of the last body-segment or telson, and arranged in three paii's, namely, a central 

 pair, 5-75 mm. long, and two outside pairs, each of which has its inner spine or 

 seta, 8 mm. long, and its outer spinule, 3'17 mm. long (see PI. XIII, fig. 9, 

 magnified). 



In his " Monograph of the Phyllopod Crustacea of North America " (' Twelfth 

 Annual Report of the U.S. Geol. Survey,' 1883), Dr. A. S. Packard figui'ed and 

 described (pp. 437, 53G, and 590, pi. xxxvi, fig. 7, and pi. xxxvii, fig. 5) the 

 cercopods of Nebalia. An embryonic N. Geoffroyi has two strong tapering cerco- 

 pods, each terminating with a long seta between two short spinose setEe. If the 

 two cercopods were reduced and united laterally, the six setce would be brought 

 together, and represent the three paired (or doubly trifid) cercopods of Hymeno- 

 caris. In other words, Hymenocaris has caudal appendages equivalent to the 

 terminal seta3 of the Nebalia referred to if these latter were brought together 

 laterally, and stood out directly from the last body-segment or telson without 

 any differentiated basal cercopods. 





