12 ARKIV FÖR ZOOLOGI. BAND 10. N:0 8. 



mandibidare does not reach symplecticum. Frontale is paired. 

 Suhorhitalia and nasalia are absent. The jaws bear teeth form- 

 ing a beak. Long slender teeth are developed on the 

 suprapharyngeals. The mouth is very small. 



In a specimen 1,5 mm. in length I found the cJiondro- 

 cranium well developed (Fig. C). Tectum cranii is large with- 

 out any fontanelle. There is a taenia tecti medialis connect- 

 ing the tectum cranii with the tectum synoticum. The tae- 

 niae marginales are very short. The antorbital plans are 

 small, but pierced by the olfactory nerves. There is a tra- 

 becula communis present in the stage in question. It does 

 not continue posteriorly into the cranial base, but ends with 

 a point. Whether the posterior end has been resorbed and 

 there has been a connection between the trabecles and the 

 parachordals in earlier stages my preparations do not indi- 

 cate. It is to be noted, however, that the trabecle is single 

 throughout its length also in at least a certain stage of an- 

 other Plectognath, Spheroides, The anterior end of the tra- 

 becle is connected with tectum cranii by a cartilaginous sep- 

 tum. The cranial base shows a large fenestra basicapsularis 

 on each side. The posterior fenestra basicranialis is large. 

 In its posterior end the chorda projects. A short cartila- 

 ginous commissure connects both the sides of the cranial 

 base anteriorly, thus separating the posterior fenestra basi- 

 cranialis from the anterior one. The latter is not bordered 

 laterally by cartilage as there is no connection between the 

 trabecle and the cranial base. There are only two semicir- 

 cular septs. Fig. C shows a diagram of the chondrocranium 

 just described. No ossifications, except in the jaws, have 

 begun in this stage. A specimen 5 mm. in length, which I 

 have examined, shows the chondrocranium somewhat more 

 developed. The basicapsular and posterior basicranial ope- 

 nings are reduced. Frontals and parasphenoid are distinct. 



Balistidae. 



HoLLARD described the skull of Balistes and Monacanthus 

 in detail, but he made several mistakes, some of which he 

 corrected in a låter paper. Göldi pointed out some of Hol- 

 lard's mistakes. Klein's paper contains several notes on 



