360 WILLIAM PATTEN. 



especially as regards size, shape of the body, the hard outer 



13. — (1) Ocular or haemal surface of the cephalic shield of a Tri- 

 lobite. (2) Same of Pterichthys. (3) Same of Bothriolepis. These 

 figures are intended to show the similarity in the arrangement of the 

 cranial plates, and of the cervical and facial sutures. (4) Diagram of 

 the neural surface of a merostomatous Arachnid, showing paired arrange- 

 ment of coxal plates, and the eyes passing from the hsemal to the neural 

 surface. (5) Hsemal surface of a Vertebrate head. — in. Metastomum. 

 s. s. Cervical suture, x.y.z. Facial suture, ex. s. Coxal sense-organs. 

 s. 0. Sense-organs. 



skeleton and its peculiar sculpturing, its concentration at the 



form the connecting links between Crustaceans and Cshes." Agassiz himself 

 was at first in doubt as to whether Pterichthys was a fish or Crustacean. 



To show still further the doubtful position of some of these primitive fishes, 

 it may be stated that recently a distinguished palaeontologist advanced the 

 opinion that forms like Bothriolepis were Ascidians ! 



