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PROCEEDINGS OF THE NATIONAL MUSEUM 



VOL. 68 



strongly developed main cusp usually with a variously modified 

 undenticulated downward extension. 



In this family the tooth consists of a main cusp followed posteri- 

 orly by a bar of greater or less length, denticulated along its upper 

 margin. Prioniodus Pander, 1856, SubpHoniodus Smith, 1907, 

 Belodus and Cordylodus Pander, 1856, and Ligonodina, new genus, 

 exhibit the structure characteristic of the family. In all these 

 genera the main cusp is well marked, but the denticulated bar ranges 



Fig. 3. — PRIONIOiDIDAE, new family 



1. Genus Prioniodus Pander, 1856. Left and right teeth of the genotype. 



Prioniodus elegans Pander, 1856. Lower Ordovician of Baltic 

 Provinces. 



2. Genus Suhprioniodus Smith, 1907. Two teeth of the genotype Siib- 



proniodus paucidentatus Smith, 1907. Ordovician (Arenig-Llan- 

 deilo, Southern Uplands of Scotland. 

 3,4. Genus Cordylodus Pander, 1856. (3) The genotype (first species) 

 Cordylodus angulatus Pander, 1856. (4) Tooth of Cordylodus rotiin- 

 datus Pander, 1856, with denticles more developed. r>oth from Lower 

 Ordovician of Baltic Provinces. 



5. Genu.s Belodus Pander, 1856. The genotype (only species) Belodus 



gracilis Pander, 1856. Lower Ordovician of Baltic Provinces. 



6. Genus Ligonodina, now genus. The genotype Ligonodina pectinata, new 



species. Upper Devonian (Rhinestreet shale of Portage), Shaleton, 

 N. Y. 



from a slight development in Coi^dylodus and Belodus to the maxi- 

 mum in Ligonodina. As in other conodonts, we believe the main 

 cusp is directed backward, making the denticulated bar a posterior 

 development. 



Genus PRIONIODUS Pander, 1856 



Typically the pick shape is well developed in this genus, the 

 main terminal cusp relatively large with both edges sharp. The 

 basal extension, although variable in length, is usually strong and 



