FROM TANGANYIKA AND KENYA 159 



Holotype and paratypes. The type material consists of numerous specimens 

 preserved in relief (but in many cases in an eroded condition) on a bedding plane of a 

 piece of hard limestone registered as no. G. 79190. A specimen represented in PI. 26, 

 fig. 16 (middle of left-hand side of figure) is taken as holotype. 



Locality and horizon. Hagardulun, 25 miles N.E. of Tarbaj, N.E. Kenya ; 

 Bathonian-Callovian, Bur Mayo Limestones. 



Remarks. This species was originally recorded (Thompson & Dodson i960 : 32) 

 as Procerithium (Rhabdocolpus) sp. The same remark applies to it as to Exelissa 

 africana, described above ; it is an Exelissa (as determined by the characters of the 

 aperture) with the ornament of a Rhabdocolpus. It is less slender than E. africana 

 but more strongly ribbed. The general form of the shell and the ornament are 

 much more similar to those of Procerithium {Rhabdocolpus) mandawaense, also des- 

 cribed above, but its costae are rather more numerous and, generally, straighter 

 than in that species and it has a greater number of spiral threads. Enough can be 

 seen of the apertural characters of P. mandawaense to show that it cannot be in- 

 cluded in Exelissa. 



Genus PARACERITHIUM Cossmann 1902 



Paracerithium lonjiense sp. now 



PL 27, figs. 6a, b, 13a, b 



Diagnosis. Shell small (height of holotype 3-5 mm.), rather stoutly conical, spire 

 angle about 38 °. Protoconch conical, with its initial whorl minute. Early whorls 

 evenly convex, later whorls with a well-marked shoulder separating a concave sutural 

 ramp, which meets the preceding whorl almost tangentially, from a feebly convex 

 outer face which on the later whorls is inclined inward abapically and on the last 

 whorl merges in an even curve with the moderately convex base. Ornament con- 

 sisting of strong, rounded collabral ribs which tend to form tubercles at the shoulder 

 on the last whorl and are crossed by spiral cords (one at the shoulder and two on the 

 outer face) separated by much broader intervals ; the base bears only spiral cords 

 which are more closely spaced than those on the remainder of the surface. Aperture 

 not preserved intact. 



Holotype and paratypes. Holotype, no. GG. 10298, ex B.P. Coll. ; several 

 paratypes (including no. GG. 10299), an but one juvenile shells. 



Locality and horizon. Mandawa-Lonji creek traverse, Mandawa area, Tangan- 

 yika ; Lower Kimmeridgian. 



Remarks. This species has the same general aspect as various representatives of 

 Paracerithium from the Jurassic of France figured by Cossmann (19136, pi. 13, figs. 

 28-63), but differs from all of them in details of ornament. 



