314 Mr. A. Smith Woodward on a 



5. PseudoxyrJiopus punctatus. 

 Xenodon punctatm, Peters, Mon. Berl. Ac. 1880, p. 221, pi. — . fig. 3. 



Stated to be from Brazil, but its habitat will probably prove 

 to be Madagascar. I am indebted to Dr. Paul Matschie, of 

 the Berlin Museum, for a sketch of the dentition of the type 

 specimen, which shows the fourth and fifth mandibular teeth 

 enlarged. 



XXXVI.— ^ Neio Theory o/Pterichthys. 

 By A. Smith Woodward, F.Z.S. 



The missing link between the Chordata and some of the 

 non-Chordate phyla below has long been sought in vain 

 among the organisms revealed by palaeontology. The almost 

 invariable destruction of soft tissues during fossilization 

 evidently constitutes the chief obstacle to the quest ; and it 

 still seems most probable that none of the intermediate types 

 developed hard skeletal parts such as could be preserved 

 under ordinary conditions. There is, however, one anoma- 

 lous group of early Palaeozoic skeletons which has been almost 

 invariably referred to in this inquiry, i. e. the tribe com- 

 prising FterichthySj Bothrioleins^ Cephalaspis, and their allies. 

 At the time of their first discovery the superficial aspect of 

 these skeletons at once led to their comparison with the con- 

 temporaneous Eurypterids, then believed to be Crustaceans ; 

 somewhat later they entered the heterogeneous order of 

 " Ganoid " fishes ; still further investigation led to a sugges- 

 tion that they might possibly be a primitive armoured form of 

 Marsipobranch fish ; and a few years ago Pterichthys and 

 Botliriohpis were compared by Cope* with the shielded types 

 of Tunicates, e. g. Chelyosoma. 



Quite recently an attempt has been made to show that this 

 gradual growth of ideas has proceeded in a wrong direction ; 

 and a well-known investigator of the morphology of Arachnida, 

 Mr. William Patten, now claims f to justify, on philosophical 

 grounds, the first impressions of the earliest collectors, lu 

 the modern acce])tation of the term, Trilobites and Merosto- 

 mata are Arachnids ; and it is in this direction, according to 



• E. D. Cope, "The Position of l^erichthijs iu the System," Auier. 

 Nat. vol. xix. (,1885), pp. 28!.)--Pl, with ligs. 



t W. Patti'u, '• C)n the Origin of Vt'ittbratt's from ArncLuiJs," Quart. 

 Journ, Micr. Sci. vol. xxxi. (18W), pp. 3o'J-30o, tig. 13. 



