NO. 3 UPPER CAMBRIAN TRILOBITE FAUNAS — RASETTI 63 



cies. Preglabellar field about as long (sag.) as border width (sag.) ; 

 border elevated, arched transversely. Palpebral area almost as wide as 

 anterior portion of glabella, less upsloping than in M. prominens ; pal- 

 pebral lobe moderately upsloping, not extending much farther forward 

 than the anterior end of the glabella. Posterior area much less tapered 

 than in M. prominens, more rounded distally, bearing a deep, wide 

 furrow. Posterior outline of cranidium transverse; posterolateral 

 angles not extending farther backward than occipital ring. 



Free cheek almost subtriangular. Border distinct for more than half 

 the length of the margin. Anterior section of facial suture much longer 

 than in M. prominens, corresponding to the more posterior position 

 of the eye. Posterior section with slight sigmoidal curvature, cutting 

 posterior margin closer to genal angle than in preceding species. Ele- 

 vated portions of surface covered with coarse tubercles, possibly repre- 

 senting the base of broken spines, those on the glabella being arranged 

 more or less regularly in several rows. Length of largest cranidium 

 5 mm. 



Discussion. — The present species resembles M. calymenoides rather 

 than M. prominens, the differences from the latter having been already 

 pointed out in the description. An accurate comparison with topotypes 

 of M. calymenoides is not very significant because of the poor preser- 

 vation of these small trilobites as internal casts in the Eau Claire sand- 

 stone. One definite difference seems to be that in AI. calymenoides the 

 anterior border has almost even width, whereas in the present species 

 it tapers at the sides. The palpebral area seems to be proportionately 

 wider. 



Occurrence. — Uppermost beds of the Maryville limestone (Cedaria 

 zone) at localities cnc/1 to cnc/6. 



Ty/^^.y.— Holotype : U.S.N.M. 144696. Paratypes: U.S.N.M. 

 144697-8. 



MENOMONIA, species undetermined 



Plate 2, figures 25-27 



A few incomplete cranidia and several free cheeks apparently repre- 

 sent a form of Menomonia different from the two previously discussed 

 species. 



Most of the cranidial features agree with M. tuberculata, except in 

 the somewhat more anterior position of the eyes, narrower palpebral 

 area, and lack of tubercles on the posterior area, where the surface is 

 finely wrinkled. The free cheek resembles more closely that of M. 

 prominens in general shape and also shows a wrinkled surface with, 

 in addition, a few tubercles on the anterior part of the border. 



