330 Prof. D. M. S. Watson on 



anteriorly into a lamina which fuses with the ))rootic. The 

 bone terminates in a transverse suture with the last of the 

 parafrontals at a point behind the middle of the [)arietal. In 

 front of this spot the parietal is continued out laterally as a 

 thin shell of bone, which in the articulated skull is completely 

 concealed by the two posterior parafrontals. From the lower 

 surface of this part of the parietal a descending process 

 reaches, and in adults fuses with, the prootic. 



As has long- been known, the narrow frontals of Macro- 

 poma are continued forward by a series of small square 

 elements, which seem to be either four or five in number in 

 different individuals. 



From the lateral borders of the lower surface of tliese 

 elements and of the frontals thin flanges of bone pass outward 

 below the parafrontals. 



The parafrontal series of bones begin at sutures with the 

 snpratemporals, and continue forwaid as straight rows lying 

 on the flanges of the parietals, frontals, and preceding bones 

 until they turn inward and meet in the middle bone imme- 

 diately behind the premaxillse. 



The number of parafrontals in each row is extremely 

 difficult to determine, and appears to be variable in different 

 individuals ; it is of the order of ten. 



There may be a median parafrontal in the front (Stensio's 

 inter-rostral), and the second of the paired series (Stensio's 

 nasalo-antorbital) is always large, although in Macropoma it 

 is never perforated by narial openings. 



Attached to the lateral margin of this large second para- 

 frontal is a remarkable and very characteristic bone, which 

 can be recognized in Undina. This bone stands nearly 

 Vertically on the side of the face. Its anterior border is 

 vertical and no doubt supported the hinder edge of the pre- 

 n)axilla. The lower border is produced downwards into a 

 long slender process, which ends freely and perhaps separated 

 the two nasal apertures. 



Above and caudally to the process the outer surface of 

 the bone is depressed and is smooth, in marked contiast 

 to the extremely rough dorsal part and parafrontals. 



The hinder end of the suture between this bone and the 

 parafrontal with which it articulates is widened out into a 

 large nearly circular hole, which, as it continues one of the 

 deep grooves on the suborbital, is certainly merely for part of 

 the lateral line apparatus. 



The suborbital is already well known and sufficiently 

 shown in tig. 5. Anteriorly it articulates with two para- 



