Formation of the Skeletal Parts in Echinoderms. 281 



II. afiicre- 



H. crisfitta. II. yaleata. australU. 



Rasftl length 188 138 151 



Zygomatic breadth 80 84 91 



Length (round curve) of nasals. . 100 99 91 



„ „ „ of frontal 31 33 47* 



Length of parietal (to extreme 



back of crest) 31 33 33* 



Breadth of nasals at anterior end 



of naso-premaxillary suture 37"5 41 32 



Breadth of nasals at posterior end 09'5 55 61 



Interorbital breadth at edge of 



lacrymals 73 62-3 76 



Interorbital breadth at rudimen- 

 tary postorbital processes . . 68'5 66"5 70"G 



Height of skull from palate be- 

 tween "^^ 70 76 73-5 



Least vertical diameter of lower 



anterior zygoma-root 5 5'5 1"7 



Palate length 77 80 87 



Mesial length of premaxillse 29 25-7 28 



These measurements sliow clearly the conspicuous differ- 

 ences between H. galeata and its allies in the relative propor- 

 tions of the two interorbital breadths, anterior and posterior, 

 in the shape of the nasals, and in the height of the skull, this 

 last being the character from which is derived the name 

 selected for the species. 



Hah. Lamu, East Africa. 



It is much to be hoped that more specimens of this inter- 

 esting addition to the fauna of our East-African possessions 

 will soon be brought to Europe, and it may be noted, as a hint 

 to collectors, that a good series of skulls of different ages 

 would be of especial value for the proper comparison of the 

 species with its allies. 



XXXIX. — The Formation of the Skeletal Parts in 

 Echinoderms. By Cael Chun, of Breslau f- 



The share of the mesoderm cells of Echinoderms in the 

 building-up of tlie elements of the calcareous skeleton is alto- 

 gether imperfectly understood. After it had already been 

 shown by the older observers that the calcareous bodies are 

 formed by the connective-tissue cells of the gelatinous central 



* Fronto-parietal suture closed and its position not quite certain, 

 t Translated from the ' Zoologischer Anzeiger,' xv. Jahrg., no. 408, 

 December 26, 1892, pp. 470-474. 



17* 



