328 Royal Society. 



tions of the form of short double cones. Ligamenta intervertebralia 

 very strong. Heptanchus (anterior vertebra). 



3rd. Vertebral bodies wholly cartilaginous, with thin osseous 

 double cones of good length in the middle of the cartilaginous body. 

 Centrophorus. 



4th. Vertebral bodies well ossified, cylindrical and strong, formed 

 inside by strong osseous double cones, and outside by alternating 

 layers of cartilage and bone. Sguatina. 



B. Sheath of the chorda thin. 



5th. Vertebral body a thin hollow osseous cylinder ; chorda pro- 

 per in its whole length cylindrical. Leptocephalus, Helmichthys, 

 Hyoprorus (last vertebra). 



6th. Vertebral bodies slightly constricted osseous double cones, 

 with external longitudinal ridges. Chauliodus, Stomias. 



TYPE II. The vertebral body is formed partly from the sheath of 

 the chorda and partly from the outer ossifying layer. 



1st. Chordal vertebral body partly cartilaginous, with a stronger 

 osseous double cone in its middle part. External part of the body 

 formed by a thin layer of cartilage from the coalesced arches, with 

 two lateral ossified plates. Heptanchus (posterior vertebrae). 



2nd. The same with/bwr external ossifications, whose ends coalesce 

 with the internal double cone. Acanthias, Scymnus. 



3rd. Chordal vertebral body nearly totally ossified, of the form of 

 a strong double cone, with strong external longitudinal ridges. Ex- 

 ternal part of the body a strong layer of cartilage with superficial 

 ossifications continuous with those of the arches. Raia, Torpedo. 



4th. Chordal vertebral body nearly wholly ossified, of the form of 

 a thick double cone. External part of the body formed by cartilage, 

 with four strong wedge-shaped ossifications uniting with the ends of 

 the inner double cone. Scy Ilium. 



5th. Chordal vertebral body a strong osseous double cone, partly 

 with external ridges. External part of the body formed by four 

 strong wedge-shaped ossifications, derived from the periosteal layer 

 between the cartilaginous arches, which in some genera totally 

 coalesce with the inner double cone, whilst in others this happens 

 only at the ends of the latter. Mustelus, Carcharias, Sphyrna> 

 Galeus. 



TYPE III. The vertebral bodies are wholly developed from the 

 external ossifying layer. 



1st. The vertebral bodies are developed from four 'cartilaginous 

 parts, viz. the superior and inferior arches. Anterior vertebrae of 

 the Raiidse. 



2nd. The vertebral bodies are developed only from two cartila- 

 ginous or osseous parts. 



. From the two neural arches, which in uniting do not enclose 

 the chorda, which lies underneath them. Cultripes pro- 

 vincialis, J. Muller, Eana paradoxa, Duges. 



