RAYMOND: sdmi \i w ORDOVICIAN TRIL0BITE8. 293 



Several yean ago Mr. A. (i. Becker, while collecting in 1 1 »< * ravine 



of B small si ream about two miles west of ( lermont , Iowa, came upon 



a slal> of limestone <>n which were two specimens of the trilobite which 

 Sh >tu in later described as Megalaspis beckeri. The outstanding feature 

 of this animal is the great elongation of the anterior portion of the 



eephalon. The elongate triangular head-shield invited a comparison 

 with such asaphids as Megalaspis extewuata (Dalman), hence the 

 generic reference. 



No one has as yet been fortunate enough to discover an hvpostoma 

 of this species, so that it is not possible to say definitely that M. 

 beckeri is not a Megalaspis, hut that it is almost certainly not one is 

 indicated by the following considerations: — 



1st. Nearly all the species of Megalaspis in the typical region in 

 northern Europe are found in the Lower Ordovician, only one or two 

 surviving till the Middle Ordovician, and none till the Upper Ordovi- 

 cian rocks were deposited. 



2nd. Megalaspis is exceedingly rare in America, while isotelids are 

 common and highly variable. 



3rd, No hvpostoma of the ogygiocarinid type has been found 

 in the Maquoketa. 



4th. The glabella of Megalaspis beckeri is not definitely outlined 

 and is long, while in all species of the true Megalaspis the glabella is 

 outlined and is relatively short. 



5th. The axial lobe of the thorax of M. beckeri is wider in propor- 

 tion to the total width than is that of any species of the true Mega- 

 laspis. 



In consideration of the above, I make Megalaspis beckeri the type of 

 a new genus, Ectenaspis, the extended or stretched out character 

 of the cephalic shield suggesting the name. This genus seems very 

 close to Isotelus, and its derivation from Isoteloides through some 

 such forms as /. angusticaudus Raymond and Ectenaspis homalono- 

 toides (Walcott) is quite probable. 



Ectenaspis beckeri is an exceedingly rare fossil in the lower part 

 of the Maquoketa (Upper Ordovician) in Fayette Co., Iowa. The 

 only other species which can now be placed in this genus is Ectenaspis 

 homalonotoides (Walcott). 



Isotelus annectans sp. now 



7.<<>!t It, i<h .< homalonotoides Raymond and Narraway (rum Walcott), Aim 

 Carnegie museum, 1910, 7, p. 52, pi. 16, figs. 9-11. 



