STROBOCERAS SULCATUM. '^1 



The siphuncle is situated very near the peripheral margin. 



The surface of the test is covered by very fine and regular lines of growth, 

 about six of which occupy the space of 1 mm. They are curved sigmoidally upon 

 the sides, and form a deep, backwardly directed sinus upon the periphery, corre- 

 sponding with the contour of the aperture. When the testis preserved these lines 

 are easily seen with a lens of low power, and though merely lines of growth they 

 are so regularly disposed as to constitute an important element in the ornamenta- 

 tion of the species. 



Affinities. — This species is nearly related to S. bisulcatnm, de Koninck, sp., but 

 differs from it in having less compressed, transversely broader whorls, more 

 strongly marked and persistent sulci on the sides, and rather closer septa. In 

 a specimen of S. bisulcatnm from Vise, Belgium, in the British Museum, the 

 diameter of which is 42 mm., the height of the outer whorl is 16 mm., and its 

 greatest thickness 11 mm. In Sowerby's type, fig. 2 of his plate (the specimen 

 representing fig. 1 is lost), in the British Museum the measurements are — height 

 of the outer whorl 10*25 mm., greatest thickness of the same 9 mm., the diameter 

 of the specimen being 25'5 mm. 



Comparing the septation of the two species, I find that in the inner whorls of 

 an imperfect though uu distorted specimen of S. sulcatum six of the septa occupy 

 the space of 8 mm., whereas in one of de Koninck's figures (' Calc. Carb.,' pi. xxvii, 

 fig. 7) of 8. bisulcatnm six septa fill the space of 10 mm. "Without giving any 

 measurements de Koninck states that the distance of the septa in these two 

 species is about equal, though the septation in his figure shows the dis crepancy just 

 indicated. My statement (' Cat. Foss. Ceph. Brit. Mus.,' pt. 2, p. 95) that 

 8. sulcatum has more distant septa than 8. bisulcatnm appears, therefore, to have 

 been erroneous. It is to be regretted also that de Koninck gives no actual 

 measurements, but only general observations, as above, on this point.^ 



Remarks. — The synonymy of this species which I have adopted requires 

 explanation, and this can only be satisfactorily given by tracing its history. It 

 was first described by Sowerby in the ' Mineral Conchology ' (1829), the specific- 

 characters being incompletely given in the diagnosis, but treated with more fulness 

 in the supplementary remarks which accompany it ; both are here appended, as 

 follows : " Discoid, minutely striated ; whorls almost wholly exposed, ventricose, 

 with two large furrows on each side and several small ones ; front concave." It is 

 further stated " the concave front is bounded by sharp edges ; there is also a sharp 

 elevation between the two furrows ; the rest of the side is gibbose, with two or 

 three very shallow broad furrows upon its most elevated part. The aperture is 

 half as long again as it is wide, its sides of course indented ; the siphuncle is 



1 I am indebted to the kindness of my friend Mr. Gr. C. Crick, F.G.S., for the measurements of 

 the British Museum specimens given above. 



