12 COPE 



chamber (atrium) which opens inferiorly ; 

 openings of alimentary canal at opposite 

 extremities ; heart tubular ; Leptocardii. 



The species of the only family, the Branchiostomidse (the 

 lancelets), are of compressed, worm-like form, and burrow 

 in the soil of the shores of all oceans. No fossil remains 

 of them have been yet found. 



Superclass IV.— CRANIATA. 



The five classes of the Craniata are defined as follows : 



I. No lower jaw nor pectoral arch. 



Internal skeleton not ossified ; Agnatha. 



II. Lower jaw and pectoral arch present. 



A, Basicranial axis not ossified, supported by a 

 parasphenoid bone ; vertebral column consist- 

 ing chiefly of intercentra ; ribs myotomic ; 



Anamnia. 



Limbs represented by many-radiate fins, 

 which are also present on the median 

 lines of the body ; a coracoid bone ; 

 heart with two chambers ; one or no 

 occipital condyle ; no internal nares ; Pisces. 



Limbs consisting of one basal element, two 

 propodials, and metapodials and digits ; 

 no median fins; lower jaw attached to a 

 suspensorium, complex ; no opercular 

 bones ; a coracoid ; heart with three 

 chambers; two occipital condyles; inter- 

 nal nares ; Batrachia. 



AA, Basicranial axis ossified ; no parasphenoid ; 



