292 bulletin: museum of comparative zoology. 



larger, as well as in the shorter and wider shields. It differs from 

 other known species of the genus in the same particulars. 



Horizon and Locality :— The holotype, a gift of Mr. A. H. 

 Becker and Mr. John H. Bradley, Jr., M. C. Z. 1,5?8, was found near 

 the top of the Maquoketa at Patterson's Spring, near Brainerd, 

 Iowa. 



VoGDESiA Raymond. 



Although proposed as a subgenus of Nileus, Vogdesia proves to be 

 one of the Asaphinae, and closely related to Homotelus and Brachyas- 

 pis. This conclusion has been reached from a study of the dorsal 

 surface, as the hypostoma has not yet been seen. Vogdesia differs 

 from both the genera mentioned in having a wider axial lobe in the 

 thorax, and little or no trace of dorsal furrows on the pygidium. The 

 type is Vogdesia bearsi Raymond, from the Chazy. Other species 

 are Vogdesia minnesotensis (Foerste) and Nileus sp. (Foerste, Bull. 

 Denison univ., 1920, 19, p. 218, pi. 23, fig. 4A, B) both from the 

 Trenton, and Vogdesia vigilans (Meek and Worthen), a common tri- 

 lobite in the Maquoketa. 



Vogdesia gigas, sp. nov. 



This species differs from V. vigilans only in that the type is twice 

 as large as the largest known specimen of the latter, the eyes are 

 farther from the anterior margin, and the test is slightly if at all punc- 

 tate. 



Measurements: — Specimen, if extended, about 120 mm. long. The 

 cephalon is 34 mm. long and 58 mm. wide; an eye is 8 mm. long and 8 mm. 

 from the posterior margin. The pygidium is 36 mm. long and 55 mm. wide, 

 with no trace of an axial lobe. The thorax is estimated to be about 50 mm. 

 long, each of the eight segments being 7 mm. wide in the enrolled state. 



Horizon and Locality: — This species is known from a single 

 specimen collected by the writer near the base of the Maquoketa on a 

 creek four miles west of Clermont, Iowa. Holotype, M. C. Z. 1,589. 



Ectenaspis, gen. nov. 



Type, Megalaspis beckeri Slocum, Field mus. nat. hist. Geol. ser., 

 1913, 4, p. 50, pi. 14, fig. 5. Iowa Geol. survey, 1916, 25, p. 196, pi. 15, 

 fig. 5. 



