NORTH STAFFORDSHIRE COAL FOSSILS. 221 



one fragment there are impressions of several small, delicate, 

 interspinous bones or fin-supports, but in none of the 

 specimens is the caudal fin preserved. The spine is about 

 an inch and a-half long, including the portion inserted 

 in the flesh, and about a quarter of an inch wide at the base ; 

 it gradually tapers to a rather blunt point. The lateral 

 edges of the spine are straight and compressed, the centre 

 slightly swollen, the surface marked with numerous short, 

 shallow, longitudinal grooves, which cover nearly two-thirds 

 of the entire length ; the remaining portion is smooth. No 

 portion of the head is preserved. It was probably carti- 

 laginous throughout. Within its area, numerous teeth are 

 shown ; in one specimen more than forty of the teeth are 

 preserved. The teeth (see plate, fig. 11) agree with the 

 type specimens figured by Agassiz (fig. 5 7, op. cit.) Ac- 

 cording to that authority, the teeth " have a base small 

 in proportion to their height, the crown rising from the 

 base in the form of a cone and very obtuse." The root 

 is short and nearly as broad as the crown, and is covered 

 with shallow cavities ; the surface of the crown is smooth 

 and generally of a dusky white enamel and finely punctated. 

 At present, very little is known of the arrangement of the 

 dental apparatus of Helodus. A specimen in our collection 

 shows a section of the mouth in which teeth of the form 

 above described are shown in- situ. They appear to be 

 arranged in rows in both the upper and lower part. They 

 probably formed a pavement-like dentition covering the 

 whole of the floor of both halves of the mouth, the undulating 

 surface of the upper half fitting exactly into that of the 

 lower half. Our collection contains many teeth which differ 

 from the typical specimen. It is probable that of these 

 there are some which are not specifically distinct, but were 

 adapted to particular parts of the mouth. It is impossible 

 to determine the relationship of these various forms until 



