lOO NEW YORK STATE MUSEUM 



and elongate ; external occipitals large ; centrals divided, the two pairs on 

 , either side not meeting in the middle line. Pineal foramen inconspicuous, 

 situated slightly in advance of a line joining the anterior borders of the 

 orbits. Sensory canals forming large tubular excavations in the bone, 

 opening at the external surface by a continuous narrow slit or by a double 

 row of pores. Parachordal cartilage and notochordal sheath ossified. 

 Dental plates and abdominal armor unknown. 



The typical genus of this family is Macropetalichthys, known by a 

 single American, and one or two European species. Some others, as yet 

 undescribed, are reported by Jaekel from the Eifel Devonic, and at the 

 same time the form described by Kayser as M. pruemensis is made 

 the type of a new genus.' The members of this family evidently stand in 

 somewhat close relation with Homosteus, all of these forms having the 

 head shield prolonged posteriorly over the nuchal region, and exhibiting a 

 decidedly primitive arrangement of cranial plates. In this latter respect it 

 is interesting to note that the median series of plates are reduced to the 

 same number as in Neoceratodus. 



Genus MACRO- ETALICHTHYS Norwood & Owen 

 This genus, certainly one of the most primitive of Arthrodires, is repre- 

 sented in this country by the typical species, which was first described under 

 the name of M. r a p h e i d o 1 a b i s. The history of our acquaintance with 

 the genus is interesting, and may be recapitulated as follows : Specimens 

 of the head shield seem to have been first discovered by Mr Joseph Sulli- 

 vant, of Columbus, O., as early as 1836. though they were not brought to 

 the attention of students until several years later. In 1846 Messrs Nor- 

 wood and Owen published a Description of a nciv Fossil Fish, from the 

 Palaeozoic Rocks of Ijidiana,^ in which the generic and specific titles were 

 properly proposed. The type specimen of M. r ap h e i d o 1 ab i s was 

 exhibited before the American Association for the Advancement of Science 



'Jaekel, O. Ueber Coccosteus und die Beurtheilung der Placodermen. Sitzungsber. 

 Gesellsch. Naturforsch. Freunde. 1902. p. 113. Il'id. Jalirg. 1906. 73-85. 

 ^Am. Jour. Sci. [2] 1846. 1:367-71. 



