INVERTEBRATE PALAEONTOLOGY. 427 



of rather prominent, subquadrangular nodes, and a few smaller ones along 

 about one-third the height from the umbilicus. 



Septa divided into rather deep lobes and sinuses; siphonal lobe longer 

 than wide, nearly oblong in form, and provided on each side with two prin- 

 cipal slender branches, the two terminal of which are parallel, longer than 

 the others, and each subdivided into two unequal, sharply, digitate branchlets, 

 while the others are scarcely more than sharply digitate; first lateral sinus 

 almost as long and wide as the siphonal lobe, nearly oblong in form, and 

 deeply divided into two unequal, variously sinuous and subdivided branch- 

 lets ; first lateral lobe narrower and shorter than the siphonal lobe, and pro- 

 vided with two nearly equal, bifid, and sharply digitate terminal branches, and 

 on each side, with one much smaller, merely tridentate, lateral branch ; sec- 

 ond lateral sinus much smaller, and proportionally narrower than the first, 

 and nearly equally divided into two deeply sinuous and more or less subdi- 

 vided terminal branches, with some smaller, nearly simple, lateral divisions ; 

 second lateral lobe not more than half as long and wide as the first, but very 

 similarly branched ; third lateral sinus much smaller than the second, and 

 divided at the end into two equal, slightly sinuate, terminal branches, with 

 some small, obtuse, lateral projections ; third lateral lobe not larger than one 

 of the terminal branches of the second, and trifid at the end, the divisions 

 being very small and nearly or quite simple. Farther in there is a minute, 

 simple projection, that probably represents the minute fourth lobe in some 

 of the other varieties. 



This shell differs from Dr. Owen's type of his S. nodosus, in having its 

 non-septate deflected portion of the last volution much shorter, and its inner 

 volutions more compressed, while the nodes near its umbilicus are decidedly 

 smaller. I have not had an opportunity to compare it with Dr. Owen's type- 

 specimen, and his figure of a septum of the same is evidently not drawn with 

 sufficient completeness arid accuracy of detail to afford a satisfactory means 

 of comparison of internal structure. Nevertheless, from the similarity of form 

 and ornamentation, I cannot doubt that our shell is not more than a mere 

 variety of the same species. 



On comparison with foreign species, our shell will be found to resemble 

 so closely some of the European forms referred to S. constrictus, Sowerby 

 (see Descrip. des Moll. Foss. Craie des Env. de Limbourg, pi. v, fig. 2, by 

 Ernest Favre), (hat there really seem to be scarcely any external characters 



