(i) 88 Palasontologia Sinica Ser. B 



Horizon and Locality: This species has so far been found only in the Machia- 

 kou limestone of Tangshan in the Kaiping basin, eastern Chihh. It is less common than 

 some of the other species. 



Actinoceras curvatum Grabau (sp, nov.) 



Plate VIII, %. (i. 



Shell gently curved, with large siphuncle close to the convex side, though not in 

 contact with the shell. The diameter of the siphuncular elements or nummuli, in the 

 only known specimen, is 12 mm. and their length 2.4 mm. giving a proportion of 1 to 5. 

 They are moderatel}^ contracted at the sejrtal crossing S(j that their narrowed portion is 

 about S mm. in diameter. Diverticula from the endosiphuncle (the latter not exposed in 

 the sepcimen) extend nearly to the outermost margin of the nummulus where there 

 appear to be rather widely-spaced mural pores, which are, however, not well shown 

 except now and then in one or another of tlie nummuli. 



There is some variation in the length of the individual nummuli, but no 

 appreciable change throughout the jiart of the shell shown, which is aliout W mm. long. 

 The average length of the nummuli remains the same so far as exposed, but the diameter 

 apparently decreases somewhat apicad, but this can not be determined with certainty. 

 The width of the shell cannot be ascertained but judging from the septa preserved, it 

 could not be less than 20 mm. in the lower part, and probably M'as 25 mm. The septa 

 are strongly oblique towards the siphuncular side. If the curvature was regular, with a 

 shell width of 25 mm., the depth of the septa \vas equal to that of two camerte. 



While the septal distance in the upper part of the shell \\as presumably that of 

 the nummuli-length, or 2.4 mm. on the average, it was somewhat greater in the earlier 

 part of the shell, where the septa are preserved. There the average is 2.7 mm., some of 

 the septa being separated by as much as 3 mm. 



Stereoplasmic thickening of the septa is moderate, being confined to the upper 

 surface of the septum and occupying one-half of the septal interspace or less. It is 

 irregular, swelling in some parts, and thinning away in others. It seems to be least 

 developed on the inner or concave side. It was apparently bounded above by a 

 pseudoseptum. 



Horizon and Locality: A single imperfect specimen has been obtained by Dr. 

 F. F. Mathieu from the Machiakou limestone of Lincheng, province of Shantung. 

 Though imperfect, it is thought worthy of description, as it is the only curved Actinoceras 



