other shark families. No attempt has been made 

 to use it here because of this and because only 

 about half the scyliorhinid genera are being 

 reviewed. 



Strasburg (1963), in discussing tooth replace- 

 ment in a squaloid species, fsistius, used the terms 

 independent dentition, alternate overlap, imbricate 

 overlap, and mixed alternate and imbricate over- 

 lap to describe the arrangement of teeth in a trans- 

 verse band and to distinguish these arrangements 

 from the modified imbricate overlap found in 

 Isistms. He found no pure alternate dentition in 

 the species he examined, but these did not include 

 a scyliorhinid. 



In scyliorhinids several transverse series of 

 teeth are functional. For the purposes of this dis- 

 cussion a series of teeth is defined as a file or array 

 of teeth along a single line running parallel to the 

 jaw cartilage axis from one corner of the jaw 

 opening to the other. A row of teeth on the other 

 hand is defined as a file of teeth in a line extending 

 from a germinal area on the inner surface of the 

 jaw to the outer rim of the jaw or lip. Rows of 

 teeth are frequently, but not always, arranged in 

 a line on a plane perpendicular to the axis of the 

 jaw cartilage. 



In all scyliorhinid sharks several series of teeth 

 are functional, and in addition two or more series 

 of developing teeth are present along the inner 

 side of the jaw. The developing teeth are covered 

 there by the lining of the mouth which forms a 

 protected space, in which tooth buds form. In 

 Scyliorhinus, Galeus, and Schroederichthys four 

 or five functional series are usually present in each 

 jaw and in Apr'tsturus five or six functional series. 

 Impressions or scars of tooth bases are often vis- 

 ible at the outer ends of tooth rows. If two series 

 are considered together as one band, the arrange- 

 ment is alternate, the teeth in the outer series being 

 present in half the tooth rows with their bases 

 overlapping the alternately occurring teeth of the 

 next functional series. The teeth of all specimens 

 of scyliorhinids examined were somewhat crowded 

 with a considerable degree of overlap (see fig. 11). 

 Alternate dentition with less crowding is to be 

 found in some sharks of other groups. The ar- 

 rangement of teeth which, following Strasburg 

 i L963), would probably be called modified alter- 

 nate dentition if found in Pristiophorus i but with 

 less crowding has a quite different appearance from 



the typical arrangements in scyliorhinids. In 

 Prist to pharus (fig. 12) the number of rows of teeth 

 are readily counted, and no confusion results from 

 the appearance of diagonal files of teeth. 



Figure 11. — Head of a 430-mni. adult male Apristurus 

 riveri showing diagonal files of teeth in the lower jaw 

 at the left side of the photograph. Dentition in this 

 specimen is alternate throughout. Reflections from 

 base of some of the teeth appear in the photograph to 

 depict accessory cusps, but in reality none are present 

 on teeth that are shown in the photograph. 



The presence or absence of a separation of the 

 teeth of one side of a jaw from teeth of the other 

 side by a band of fleshy material seems to be a 

 variable in the scyliorhinid specimens examined. 

 Many specimens of Apristurus have such a sepa- 

 ration either in the upper or lower jaw or both, 

 whereas some do not. Furthermore this vari- 

 ation occurs in series of the same species. The 

 extent to which this variation may be the result of 

 stretching of ligaments at the symphysis has not 

 been determined. 



The number of tooth rows in some scyliorhinids 

 is difficult to count for a variety of reasons. The 

 teeth are small, and toward the angles of the jaws 

 low-crowned multicusped teeth are not clearly de- 

 fined. The teeth are crowded, and in a few speci- 

 mens, or perhaps a few species, the arrangement of 

 the teeth is not a simple alternate arrangement but 

 is mixed. Similarities between the cat sharks, 



594 



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