lxxviii PROCEEDINGS OE THE GEOLOGICAL SOCIETY. [May 1 895, 



the middle line. "Walcott described the thoracic appendages in 

 Oalymene as slender six-jointed walking-legs (endopodites) with a 

 single pointed termination, the basal segment giving rise to a branch 

 appendage (exopodite). On each side of the thoracic cavity he 

 also described a row of bifid spiral appendages, of the nature of 

 gills, and he suggested that branchiae were attached to the bases 

 of the thoracic limbs as well. The abdominal or pygidial rings 

 carried appendages, a pair to each segment, but they do not appear 

 to have differed from the thoracic limbs, save in size. The mouth is 

 situated behind the hypostome, and has four pairs of jointed mandu- 

 catory organs, the bases of which are modified to serve as jaws ; 

 the hindmost pair being the largest, and expanded at the distal 

 extremity into a swimming-organ. 



The correctness of Billings's views, as to the nature of the 

 thoracic limbs of AsapTius platycephalus, was further confirmed by 

 the finding of a specimen of Asaplms megistos, in the Ordovician 

 rocks of Ohio, which shows the under surface with its appendages, 

 and has been described by Dr. I. Mickleborough. 1 This specimen 

 shows two pairs of maxillipeds or jaw-feet, eight pairs of walking- 

 appendages, corresponding to the eight pairs of free thoracic 

 segments, each limb having about six joints. The under side of 

 the coalesced segments of the abdomen (pygidium) reveals a series 

 of from 12 to 16 similar paired appendages, diminishing rapidly in 

 size from before backwards to the extremity. A broad median 

 groove extends along the under side of the thorax and abdomen, and 

 probably represents the space once occupied by the sternites or, 

 possibly, the straight intestinal canal, observed by Barrande in some 

 trilobites from Bohemia. Traces of supposed branchial filaments 

 have also been observed in this specimen, apparently attached to 

 the thoracic legs. 



No further addition had been made to our knowledge of the 

 appendages of trilobites until July 1893, when Mr. W. D. Matthew, 

 a student of Columbia College (N.Y.), communicated the result of 

 his examination of several specimens of Triartlirus Beckii, obtained 

 by Mr. W. S. Valiant from the ' Hudson Biver Shales ' (Ordo- 

 vician), near Borne, New York. 2 After recording the extent of our 



1 Journ. Cinciunati Society Nat. Hist. vol. vi. (1883), & Geol. Mag. 1884, 

 p. 80. 



2 See Trans. New York Acad. Sci. vol. xii. (1893) pp. 237-241, pi. viii., 

 ' On Antennae and other Appendages of Triarthrus BecJcii' by W. D. Matthew, 

 July 17th, 1893. 



