I 14 WILLIAM PATTEN. 



into the lateral folds, although no such folds have been detected 

 in the trunk region. 



There are no indications whatever, in either surface views or in 

 sections of vertebral centra or arches, and the preservation of the 

 specimens is so perfect, that there is every reason to believe such 

 structures, even if formed of cartilage only, were absent. Neither 

 have we found any indications of a notochord, although one may 

 infer from the outline of the trunk that a notochord was present. 

 It was probably surrounded by a membranous sheath of no more 

 consistency, if as much, than that in Amphioxus. 



Several specimens show a remarkable membranous frill pro- 

 truding from the ventral and lateral margins of the posterior 

 opening of the buckler. It extends completely across the ven- 

 tral surface like a curtain, and is entirely separate from the over- 

 lying trunk. The lateral margins vary a good deal in different 

 specimens, but, when clearly shown, they extend backwards in 

 long lobes, which in one specimen are clearly thrown into regular 

 folds like those indicated in the restoration. On the sides and 

 toward the dorsal surface, the membrane appears to be reduced 

 to a narrow fringe projecting from the inside margins of the open- 

 ing of the shield, Fig. 2. 



The ventral surface of the trunk extends without interruption 

 or attachment over the frill and for about an inch over the vis- 

 ceral surface of the posterior ventrals. Here there is a prominent 

 transverse ridge and a large scar on either side, probably the 

 places of attachment of the trunk to the shield. 



A large but very thin and nearly circular scale, or plate, 

 marked with deep-lying radiating lines and with superficial con- 

 centric ridges is attached to the ventral surface of the trunk, 

 between it and the inner surface of the posterior ventrals. The 

 opening to the cloaca lies just above this plate, Fig. 2. 



All the sectioned specimens showed the presence inside the 

 buckler of a peculiar core, about an inch and a half long and 

 half an inch in diameter, Fig. 2. It varies in shape in different 

 individuals, but in all of them it has essentially the same charac- 

 ters and the same location in an antero-posterior direction. But 

 its position shifts from side to side as though it were suspended 

 in a rather large space and free to move laterally, or in a dorso- 



