BRANCOCERAS ORNATISSIMUM. 133 



Description. — Shell discoidal, compressed, with closed umbilicus; greatest 

 thickness at about one-fourth of the height of the whorl from the umbilicus, al)out 

 seven-tenths of the diameter of the shell; height of outer whorl a])out three-filths 

 of the diameter of the shell. Numljer of whorls unknown ; inclusion complete. 

 Sides very slightly convex, merging in the narrowly rounded and somewhat 

 truncated periphery. Umbilicus closed with a callus, which extends to the centre 

 of a shallow funnel-shaped depression. Whorls subcordate in cross-section. 

 Body-chamber unknown, the septate portion alone being present in the sok> 

 individual found. 



The septation is clearly exhibited, not only by the removal of the test, l)ut also, 

 owing to a fortunate transverse fracture, the greater part of a septum is exposed, 

 tlius giving an interior view, which shows the digitate form of the loljcs and the 

 cavities left between them (PI. XXXVII, fig. 1 h). 



The ornamentation is well marked and very elegant; it consists of distinct 

 I'aised lines or fine ril)s, separated by spaces which are a little wider than the 

 latter. The ribs are from about •75 to 1 mm. apart. Proceeding from the 

 umbilicus they describe a wide-spread, forwardly directed curve, wliich merges in 

 a greatly narrowed and backwardly directed sinus upon the periphery, indicating 

 a deeply indented hyponomic sinus. The siphuncle is seen in section in the centre 

 of the peripheral lobe, where it has a diameter of 2 nnn. 



Dimensions. 



Type specimen in 



Mnseiun of Science and 



Art, Dublin. 



Diameter of shell . . . . (38 mm. 



Height of outer whorl (dorso-ventral) . . 41 '5 „ 



„ above preceding whorl . . . 23 ,, 



Thickness at umbilical marofin . . .4(3 ,, 



'&' 



Afflnitie--!. — Among the species belonging to this genus hitherto described there 

 is none that can be strictly compared with the present one. 



The Belgian Carboniferous species, Brancoceras rotatorivrn, de Kon.,^ sp., 

 resembles the latter in its rather depressed form and closed umbilicus, l)ut the 

 sutures differ in a marked degree. As de Konmck's species is only represented by 

 an internal cast, no comparison can be made of the ornaments of the two species. 



RemarJcs. — This beautiful form, the only one known to occur in the British 

 Isles, is represented by the specimen which is the subject of the above description. 

 Its true affinities had not been recognised until Mr. Crick, in looking over the small 

 collection of Goniatites in the Geological Survey Collection (Dublin Museum of 



1 " Fauue Calc. Carb. Belg.," 1880 (' Ann. Mus. Roy. d'Hist. Nat. Belg.,' torn, ii), pt. ii, p. 94, 

 pi. xlvii, fig. 12. 



