58 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 148 



BLOUNTIA BRISTOLENSIS Resser 



Plate 10, figures 1, 2; plate 11, figures 9-12 



Blountia bristolensis Resser, 1938a, p. 65, pi. 12, fig. 24. 

 Maryvillia bristolensis Resser, 1938a, p. 87, pi. 12, fig. 38. 



Blountia nixonensis Lochman, in Lochman and Duncan, 1944, p. 43, pi. 4, figs. 

 7-12. 



Available material. — The hypodigm of B. bristolensis includes the 

 holotype pygidium. Maryvillia bristolensis is based on a cranidium 

 from the same collection. Blountia nixonensis was described from 

 numerous cranidia and pygidia. The author's collections include nu- 

 merous fragments and one articulated shield. The latter allows a de- 

 scription of the thorax. 



Description. — Entire exoskeleton ovate ; pygidium as large as ceph- 

 alon. Thorax of 7 segments, not tapered, as wide as cephalon and 

 pygidium. In the specimen, evidently an exuvia as it lacks the free 

 cheeks, the cranidium was pushed over the thorax, concealing 

 the entire first and part of the second thoracic segment. The entire 

 thorax was exposed during preparation when the cranidium broke off. 

 In the illustration the cranidium is shown restored. Thoracic axis 

 slightly tapered, at much lesser rate than pygidial axis. Axial furrows 

 on thorax rather deep. Pleurae unfurrowed, flat and horizontal in 

 proximal two-thirds, presenting sharp geniculation and showing an- 

 terior facet that allowed enrollment of the animal. Termination of 

 pleurae narrowly rounded, sharper in anterior pleurae. Length of exo- 

 skeleton, allowing for displacement of cranidium, 17.4 mm., of which 

 7.0 belong to the cephalon, 4.4 to the thorax, and 6.0 to the pygidium. 

 The individual corresponds almost to the largest size of cranidia and 

 pygidia in the author's collections. 



Discussion. — A species of Blountia common in the basal beds of the 

 Aphelaspis zone in Tennessee is identified with B. bristolensis. This 

 and Maryvillia bristolensis, from the same collection, obviously are 

 conspecific. Careful comparison of the author's material with B. nix- 

 onensis from Montana failed to reveal any differences. 



The species, like B. mimula, has 7 thoracic segments. In the present 

 case one may be certain that the individual is a holaspid. However, it 

 should not be inferred that all species of Blountia have 7 segments. 

 An undescribed Blountia from the Murphy's Creek formation of the 

 Gaspe Peninsula of Quebec, collected by the author, has 9 thoracic 

 segments. This Blountia occurs in association with Cedaria and Crepi- 

 cephalus and is therefore considerably older. 



Occurrence. — Type locality for Blountia bristolensis and Maryvillia 



