ACROTKETID^. 643 



tM material -available has a length of 8 mm. and a width of 10 mm. The average size is 

 fmm 5 to 6 uaca. in length, with a greater width. 



The Ulterior of the ventral valve shows a rounded, slightly depressed visceral area, which 

 forms a semicircular area about the well-defined apical callosity and pedicle opening; back of 

 the latter the false area is usually clearly defined. From each side and a little back of the 

 pedicle opening in the ventral valve a rather strong main vascular sinus arches outward and 

 then forward to the anterior half of the valve, where it divides into two or more branches; 

 numerous lateral sinuses branch off and extend nearly to the margin, and a few shorter branches 

 extend toward the central section. In the dorsal valve the vascular markings include the 

 main vascular sinuses, which extend obliquely forward and outward, and an elaborate series 

 of canals that originate in advance of the visceral area (PI. LVI, figs. Id and If). 



Our information as to the muscle scars of the ventral valve is limited to a suggestion of 

 small cardinal scars on each side of the false area a little back of the main vascular sinuses. 

 In the dorsal valve small cardinal scars (cl) occur on each side of the median ridge back of 

 the base of the main vascular sinuses ; small centrals (h) also occur on each side near the 

 anterior end of the median ridge. 



Observations. — The above description is made from the study of a large number of speci- 

 mens from several locahties in Sweden, and a fine locality on Bornholm Island, Denmark. 

 It differs somewhat from Linnarsson's [1876, p. 21], chiefly as the result of my having more 

 and somewhat better preserved material for study. He describes an umbonal muscle scar 

 in the dorsal valve, but from his illustration [1876, PI. IV, fig. 48b] I am inclined to think that 

 the scar is only a bit of the false area, the inner shell having been exfoliated. 



The relations of the species are with Acrothele {Redlicliella) granulata (Linnarsson) , from 

 which it differs in smaller average size, more finely granulated surface, and, what is of more 

 value, in the form of the muscle scars of the dorsal valve. 



This type of Acrothele is widely distributed. It is represented in Bohemia by A. hohemica 

 (Barrande) and A. quadrilineata Pompeckj ; in France by A. hergeroni Walcott; in North Amer- 

 ica by A. matthewi (Hartt) and its varieties; and in China by A. matthewi eryx Walcott. 



Formation and locality. — ^Passage beds between the Upper Cambrian and the Ordovician: (8x) Limestone 

 at Slemmestad, about 3 miles (4.8 km.) southwest of Christiania, Norway. 



TTpper-Middle Cambrian: (310i) Passage beds between the Middle Cambrian Paradoxides forchhanvmeri zone 

 and the Upper Cambrian Olenus truncatus zone at Borgholm, Oeland Island, Sweden. 



Middle Cambrian:" (Ifiliamd 334h) Limestones of Paradoxides forchhammeri zone at Borregaard; (161) limestones 

 of Paradoxides davidis zone at Borregaard; (334b) 6 Andrarum limestone at Borregaard; (334c) 6 in the Paradoxides tessini 

 zone at Borregaard; (334d) 6 in the zone with Agnostus parvifrons at Borregaard; (334f) limestone on Bornholm Island; 

 (16j) limestone of Paradoxides forchhammeri zone at Laesaa; (16k) limestones of Paradoxides davidis zone at Laesaa; 

 (334e) Andrarum limestone at Laesaa; all on Bornholm Island, Denmark. 



(8w) Limestones of the Paradoxides forchhammeri zone, at Andrarum, 20 miles (32 km.) northwest of Simris- 

 hamn, Province of Christianstad; (320o)c Limestone band between the Holmia kjerulfi zone and the Paradoxides tessini 

 zone at Andrarum, 20 miles (32 km.) northwest of Simi-ishamn, Province of Christianstad ; (320f) limestone at Andrarum, 

 20 miles (32 km.) northwest of Simrishamn, Province of Christianstad; (3201) drift blocks from the Paradoxides celandicus 

 zone at Lillviken, near Oestersund, Jemtland; (320m) " limestones of the Paradoxides forchhammeri zone at KinnekuUe, 

 northeast of Lidkoping, Province of Skaraborg; (320n) limestones of the Paradoxides forchhammeri zone at Lovened, 

 Djupadal, 19 miles (30.6 km.) south-southeast of Skara, Province of Skaraborg; (321q) limestones of the Paradoxides 

 forchhamTYieri zone at Munkesten, north of Hunneberg, Province of Skaraborg; (320r) limestones of the Agnostus Isevi- 

 gatus zone, at Hunneberg, western boundary of the Province of Skaraborg; (320y) limestones of the Paradoxides forch- 

 hammeri zone at Gudhem, 12.5 miles (20.1 km.) south-southeast of Skara, Province of Skaraborg; (320b) limestone 

 forming 2d of the Paradoxides zone, the Agnostus Isevigatus horizon, at Gudhem, 12.5 miles (20.1 km.) south-southeast 

 of Skara, Province of Skaraborg; (320v)c in the Paradoxides forchhammeri zone at Lanna, Hjulsta, Vinala, and Vrana, 

 all four in Nerike; (320p) « limestones of the Paradoxides forchhammeri zone at Sodra Mockleby, southern part of Oeland 

 Island; (320g) limestones of the Paradoxides forchhammeri zone at Borgholm, Oeland Island; and (320(i) limestone form- 

 ing 2c of the Paradoxides forchhammeri zone, at Alunbruk (alum works), southern part of Oeland Island; all in Sweden. 



(324b) Shales of Etage Ic [Brogger] at KrekUng, in Sandsvar; (334c) shales of Etage Id at Krekling, in Sandsvar; 

 and (324a) shalo of Etage Ic [Brogger] at Skrena, Skiensdalen; all [Christiania Univ. Min. Inst. Coll.] in Norway. 



<2 This species also occurs in Locality 3201i. ' Gronwall, 1902, p. 40. " Linnarsson, 1876, p. 23. 



