262 Part III. — Twentieth Annical Report 



plates of the deutaries are Avell seen ; that of the lythe is distinctly 

 greater than that of the saithe, especially anteriorly, while the plate of 

 the cod is in its turn narrower than that of the saithe. There is also a 

 distinct separation between the three forms in respect of the angle at 

 which the upper hind ramus of the dentary rises. In the cod it slopes 

 upwards very gently from the line of the tooth area, while in the lythe it 

 breaks sharply upwards ; in the case of the saithe an intermediate con- 

 dition is present. In the side view of the cavity which receives the long 

 process of the articular distinct differences are seen. A small area of the 

 inner side of this cavity is seen posterior to the outer border in the lythe, 

 a larger area is shown in the cod, and a still greater in the saithe. This 

 is due mainly to the fact that the inner side of the cavity is carried 

 farther posteriorly in the saithe than in the cod, and in the cod than in 

 the lythe. The outside of the cavity is shorter in the lythe and saithe 

 than in the cod. 



The large barbel of the cod is a marked point of difference between that 

 form and the saithe and lythe. lu the two latter there is only a small 

 barbel formed by the union of two cartilage elements which arise, one 

 from each dentary. In the lythe the barbel does not project outside tlie 

 skin, and in the saithe there is only a minute soft barbel. 



Premaxilla (pr. M.). 

 Cod, Fig. 41, PI. X. : Saithe, Fig. 14, PI. X. : Lythe, Fig. 3, PL IV. 



The same characters as regards the size of the teeth which served to 

 distinguish the dentaries of the three forms are useful as a means for 

 separating the premaxilla? also. The teeth are, however, much more 

 numerous in the latter. In the saithe there are at the part next the 

 symphysis as many as 9 to 12 rows; the toothed area becomes narrower 

 the further it extends along the premaxilla until it is reduced 

 to a single row, which is the outermost row. The tooth- sockets are 

 small, those in the hind rows being the smallest, and the sockets 

 increase in diameter towards the outer row. In the dentary the hind 

 row had the largest teeth. The toothed area on the premaxilla is shorter 

 than that on the dentary in the saithe ; they are of about the same length 

 iu the lythe ; and in the cod that of the premaxilla is of the same length 

 or a little larger than that of the mandible. The toothed area occupies 

 about six-sevenths of the length of the premaxilla in the saithe, about 

 nine-tenths in the lythe ; and in the cod it extends almost to the end of 

 the bone. In the lythe there are fewer rows of teeth than in the saithe. 

 The teeth are, however, larger, especially so in the outer row. As many 

 as six teeth are made out in a cross-section of the head of the pre- 

 maxilla (next to the symphysis), but they are usually fewer in number. 

 In a small female lythe measuring 36 cm., in the broader part of the 

 toothed area there were three rows ; in the dentary there was one row 

 only. The huge teeth in the outer row on the premaxilla of the cod at 

 once separate it from those of the saithe and lythe. As in the other two 

 species, the hind teeth are the smaller. 



In general shape, looked at from below, the premaxillae of the saithe 

 and lythe are more curved than that of the cod. In side view the 

 vertical process (or plate) on the posterior third of the bone is long and 

 rather narrow in the cod in contradistinction to those in the saithe and 

 lythe, which are roughly of a truncated triangular form. In two equally- 

 sized premaxillse of the saithe and lythe, the rounded projection on the 



