314 
Mr. A. Smith Woodward on a 
5. Pseudoxyrhopus punctatus. 
Xenodon punctatus , 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. 
XXXYI. — A New 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 PterichthySy Bothriolepis , Gephalaspis , 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 
u 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 
Bothriolepis 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. In 
the modern acceptation of the term, Trilobites and Merosto- 
mata are Arachnids ; and it is in this direction, according to 
* E. D, Cope, “The Position of Pterichthys in the System,” Amer. 
Nat. vol. xix. (1885), pp. 289-291, with figs. 
t W. Patten, “ On the Origin of Vertebrates from Arachnids,” Quart. 
Journ. Micr, Sci. vol. xxxi. (1890), pp. 359-365, fig. 13, 
