N. ROSÉN, STUDIES ON THE PLECTOGNATHS. 19 



Epioticam. Klein states that the epiotics are covered 

 by the parietals but I have not been able to find distinguish- 

 able such elements either in adult specimens or in young 

 ones (18 mm. in length). 



Prooticum present. 



Syhenoticum. Sections of specimens 18 mm. in length 

 show that this bone originated as two elements: a dennosphe- 

 noticum and an autosphenoticum in the same mode as, e. g., 

 squamosum. 



Squamosum is formed by the fusion of a dermosquamosum 

 and an autosquamosum. 



Parietals present. Frontals paired. 



Parasphenoideum is present, but there are no distinct 

 basisphenoideum and alisphenoideum. 



Vomer is clefted anteriorly. It reaches the palatines. 



Supraethmoideum and ethmoideum laterale do not reach 

 the praemaxillaries. 



Prae7naxillare. The medial surfaces of the two bones 

 with processes which lock into each other. 



Maxillare is large. Its ventral end lies lateraljy to the 

 praemaxillare. 



Palatinum. In a specimen 18 mm. in length there is 

 only an autopalatinum developed. No trace of a dermopala- 

 tinum is to be found in that stage. Palatinum articulates 

 with praemaxillare and maxillare, which form a common ar- 

 ticular surface for this purpose. 



Ectopterygoideum, entopterygoideum, metapterygoideum, qua- 

 dratum, symplecticum and hyomandihular are developed. Syrti- 

 plecticum and hyomandihulare do not reach each other. 



Suhorhitals and nasals are absent. 



In the lower jaw dentale, articulare and angtdare can be 

 distinguished. Articulare develops as an autarticulare and a 

 dermarticulare. The Meckelian cartilage is a short and slender 

 cartilaginous rod in a specimen 18 mm. in length, except its 

 angular process, which is comparatively thick. 



Praeoperculum, opercidum, suhopercidum and interopercu- 

 lam are developed. Interoperculum is rod-like, enlarged in 

 the middle. 



The hyal arch does not show any peculiarities. The first 

 branchiostegial ray is enlarged and lamelliform. 



The jaws bear teeth, which have coalesced into crests. 



