598 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxv. 



All of the specimens illustrated are f r.om the ParadoxJdrs forch- 

 hannnerl zone. They appear to be identical with the lig-ures of A. socialis 

 of Dr. Linnarsson, but not of Dr. v. Seebach. Those of the latter 

 represent a shell with strong concentric strife and median groove on 

 the false area, characters that Dr. Linnarsson says he did not find on 

 his specimens. Among- the collections made for me by Mr. G. 

 Schmalensee, collector of the Geological Survey of Sweden, 1 find a 

 larger Acrotreta than the one described b}' Professor Linnarsson. 

 which agrees with the description of A. sociaUs of Dr. v. Seebach and 

 with his figures. Dr. Linnarsson writes that he thinks Professor 

 V. Seebach had representatives of several species before him when he 

 wrote his notes on A. socialis. With this I am in full agreement, but 

 with the collections now before me from Bornholm and Oland, 1 think 

 the specific name A. sociaJis should be given to the larger shell illus- 

 trated by Professor v. Seebach. and a new name to the sma1l<n' and very 

 distinct shell illustrated by Dr. Linnarsson. In recognition of the 

 faithful and intelligent work of Mr. Schmalensee I take pleasure in 

 naming the species in his honor. 



A. schmalensei is of the type of A. subconica Kutorga. l>ut is much 

 less elevated. It may be compared with A. microsco2nca and A. (n^mma 

 among American species. 



Formation and locality. — Middle Cambrian, Paradovidts forcliham- 

 meri zone, Island of Bornholm. Andrarum and Markarten and Lov- 

 ened, Djupadalen, Vestergothana, Sweden: Borregaard. Bornholm. 

 Denmark. Paradoxides olandicus zone. Windjuelandet. Kingsaker, 

 Norway. 



ACROTRETA SEEBACHI, new species. 



Among the fragments of trilobites in the Ceratopygt limestone col- 

 lected by Mr. Schmalensee there are a few specimens of a species of 

 Acrotreta distinct from A. schmalensei and A, socialis. The pedicle 

 valve is relatively low, with the false area nearly vertical. A cast of 

 this valve shows the cardinal scars on each side high up toward the 

 apex, small main vascular sinuses, and apical callosity. False area 

 rather large and marked by a slight indication of a median depression 

 that is recognized by a slight undulation in the transverse strife. Sur- 

 face marked by fine thread-like concentric strife and lines of growth. 

 A broken brachial valve has a broad median sulcus and a small, dis- 

 tinct beak at the posterior margin. The valves are slightly trans- 

 verse. A large pedicle valve measures 3 nun. in width by 2.5 mm. in 

 length. 



The surface strife and the cardinal scars serve to distinguish this 

 species from others known to me. Acrothele ceratopygonnm Brogger 

 is from the Ceratoj:)yge shales, but it has a low pedicle valve, with the 

 false area sloping forward. 



Formation and locality. — Ceratojyyge limestone, Slemmestad, etage 



