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



formed by the basilar plate. A rostrale is present. The 

 palatoquadrate is well developed. The Meckelian cartilage 

 is short and its articular end is in the specimen in qiiestion 

 already to a great extent replaced by bone. Our knowledge 

 of the configuration of the chondrocranium of teleostean fa- 

 milies is very limited. Only a few forms of teleosts have 

 been studied from this point of view. The chondrocranium 

 best known are those of the salmon and Gasterosteus. When 

 we compare these with Spheroides we find that the most 

 pregnant characters of the latter form are: the large cranial 

 fontanelle, the single trabecle, which does not reach the ba- 

 silar plate, the well-developed nasal septum, which forms a 

 wall between the anterior parts of the orbits, the membran- 

 ous roof of the posterior portion of the posterior canal for 

 the eye muscles, the presence of only two semicircular septs 

 as in Gasterosteus. A comparison with the chondrocranium 

 of Mola described above shows several similarities. The tra- 

 becle is in both species undivided posteriorly and does not 

 reach the cranial base. The number of the semicircular septs 

 is the same. The fenestra basicranialis posterior is long and 

 narrow. Tectum cranii is different in that the large fonta- 

 nelle in Spheroides is absent in Mola. A taenia medialis is 

 present in both, but in Mola it reaches the cranial margin 

 of tectum synoticum. 



The bony elements have been described by Hollard and 

 Klein. In the following I shall give a short account of the 

 results of my studies, which are based on specimens of Sphe- 

 roides testudineus. 



Supraoccipitale. In a specimen 18 mm. in length this 

 element consists of a thin bony lamella on the exteriör sur- 

 face of tectum synoticum, provided with a feeble crista. 



Basioccipitale exists in a specimen 18 mm. in length in 

 the form of a bony lamella on the exteriör surface of the 

 posterior part of basis cranii. On the interiör surface of the 

 cranial capsule a very thin lamella is developed. In this 

 stage there is no indication of a paired origin. 



Occipitale laterale is rather well ossified in a specimen 

 18 mm. in length. It is developed mainly in the region of 

 the foramen for n. vagus; but the medial membranous wall of 

 the posterior portion of the auditive capsule has also ossified. 

 The two bones reach each other in the dorsal median line. 



