SUBCLASS II EUCEUSTACEA— PHYLLOCARIDA 749 



with a movably articulated rostral plate. Eyes pedunculate ; thoracic limbs foliaceous ; 

 no brood-plates (oostegites) ; first four pairs of abdominal limbs biramous, last two 

 piairs reduced. 



This definition is based on the characters of the Recent genus Nebalia 

 (Fig. 1452) and its allies, which Packard first grouped together under the 

 name Phyllocarida with the fossils described below. Many of the fossils, 

 however, show important differences from the Recent genera {e.g. in the 

 number of abdominal somites) which may eventually require the establishment 

 of new orders if they are to be retained within the division of Phyllocarida. 



Cephalic appendages have not been satisfactorily determined in any fossil 

 species, although traces of them have been noticed in a few genera (Cryptozoe, 

 Ceratiocaris, Bhinocaris). In the absence of contrary evidence there is reason 

 to suppose that the appendages of the head, thorax and abdomen were 

 after the type of Nebalia, since there is close correspondence in the form of 

 carapace, rostrum and abdomen. Owing to the non-preservation of limbs, 

 distinctions within the group are based principally on diff'erences in the 

 structure of the carapace, and in number of body - segments. Several 

 fossil genera (Echinocaris, Bhinocaris, Mesothyra) bear 

 a distinct optic node or pit, suggesting a sessile 

 simple eye in contradistinction to the stalked facetted 

 eye of Nebalia. In these genera, also, large cuspidate 

 masticatory organs (Fig. 1451) have been found, 

 which were apparently attached only by means of 

 muscles ; these are compared by H. Woodward with 

 the gastric teeth of the lobster. From the Middle 

 Cambrian of British Columbia Walcott has described 

 wonderfully preserved specimens of Phyllocarida 

 (new species of Hymenocaris, etc.) showing append- fig. 1451. 



ages, which will probably repay more detailed Gastric teeth of EcUnocans 



, • , • punctata Hall. Hamilton : 



investigation. Pratfs Fails, New York. %. 



Suborder A. NEBALIINA Clarke. 



Carapace folded, univalved and rostrate. 



Family 1. Nebaliidae Baird. 



Cephalic appendages five, thoracic eight, abdominal eight, terminating in two caudal 

 spines. No metamorphosis; development direct. 



Nebalia Leacli (Fig. 1452). Represented by a few marine species inhabiting 

 shallow waters. Paranehalia and NebaUopsis are also Recent and marine. 



Akad. Wissens., 1885. — Ibid., 1886. — On Occurrence of a New Form of Discinocaris in Bohemia. 

 Geol. Mag., 1892, dec. 3, vol. ix. — Sars, G. 0., Report on the Phyllocarida (Leptostraca). Kept, 

 Challenger Expedition, 1887, vol. xix. — Hall, J. and Clarke, J. AL, Palaeontology of New York, 

 1888, vol. vii. — Whitfield, R. P., New Genus of Phyllocaridae. Bull. Airier. Mus. Nat. Hist., 

 1896, vol. V\n.^Jones, T. R., and Woodvxt7-d, H., Monograph of the British Palaeozoic Pliyllopoda 

 (Phyllocarida, Packard), Part iii. Palaeontogr. Soc, 1898. — Clarke, J. M., Some Devonic and 

 Siluric Phyllocarida from New York. 54th Ann. Kept. N.Y. State Mus., 1900 (1902). — Tr«/co«, 

 C. B., Middle Cambrian BranchioiDoda, Malacostraca, Trilobita and Merostomata. Smithson, 

 Misc. Coll. 1912, vol. Ivii. No. 6. 



