N. ROSÉN, STUDIES ON THE PLECTOGNATHS. 15 



characters are the following. The jaws are very small, while 

 the ethmo-sphenoideal region is very large. The skull is 

 compressed. Squainosum is pressed down, so that it is ver- 

 tical. The supraoccipital is removed cranially. The epiotics 

 and lateral occipitals reach the dorsai median line and take 

 part in forming the roof of the posterior portion of the 

 cranial cavity. The skull of Monacanthus is to be regarded 

 as a shull of Balistes, somewhat modified. The supraoccipital 

 is displaced more anteriorly than in Balistes, which is com- 

 bined with cranial removal of the anterior dorsai fin. Para- 

 sphenoideum is smaller in Monacanthus than Balistes. 



Triacanthidae and Triodontidae. 



As I have not had an opportunity to examine te skulls 

 of these two families, I must confine myself to quote Hol- 

 LARD, Dareste and Klein. The skull seems to agree in 

 most points with that of Balistes. Praemaxillare and maxil- 

 lare are united in Triacanthus only at two points. Triacanthus 

 has well developed frontals, but lacks a supraoccipital spine. 

 The first dorsai spine inserts not so anteriorly as in Balistes. 

 Triodon has a depressed skull, which gives its configuration 

 a strong likeness to that of the Tetrodontids. Hollard 

 refers this genus to the Gymnodontids, though he points out 

 several characters common to Triodon and the Balistids. 

 The teeth of Triodon have coalesced so that they form crests. 

 Praemaxillare and maxillare are stated to be united. Accord- 

 ing to Dareste the two dentals have coaleseed in Triodon, 

 while the praemaxillaries remain distinct. Triacanthus has 

 the palatine firmiy united to the skull. According to Klein, 

 basisphenoideum and alisphenoideum are present in Triacari- 

 thus. The ventral ends of the alisphenoids reach each other 

 in the median line and »teilen durch eine Briicke, in der sich 

 die innern Ränder verbinden, den Ausgang der Hirnhöhle in 

 ein rundes Loch iiber dem sphenoid. sup. (= basisphenoid.) 

 und eine obere Spalte unter frontale» (p. 150). 



Tetrodontidae, 



The account of the skull of the Tetrodontids I shall give 

 here is based on an examination of skeletons of adult speci- 



