76 J. StarJiie Gardner-' — Cretaceous Gasteropoda. 



British. Their fossil range is extremely uncertain, as they are only 

 doubtfully represented prior to the Cretaceous period. 



Kibbed and turreted shells seem to have made their appearance as 

 far back as the Silurian age, and one species at least has been as- 

 signed 'to the genus Scalaria. Dr. Klipstein's collection from the 

 Trias, in the British Museum, embraces many shells which are both 

 -turreted and have transverse ribbing; they are variously named 

 CeritMum, Turritella, and Chemnitzia. It has already been suggested 

 by many as extremely probable that the Cretaceous Scalidce are 

 the descendants or representatives of the CJiemnitzice of older rocks, 

 a sufficiently probable supposition, and one which would carrj^ their 

 traceable ancestry to a remote period. 



The origin of the famity, as now defined, cannot with any degree 

 of certainty be traced further back than the Cretaceous era,' the 

 doubtful species found in the Jurassic series appearing to be more 

 allied to Chemnitzia. The Cretaceous Scalidce have not the strong 

 characteristics presented by the Tertiary and recent forms, seldom 

 possessing a complete peristome, and never the sharp and well- 

 defined ribs so frequently present in the latter. Some Australian 

 forms approach nearer to these fossils in this respect. 



Whilst recent and Tertiary Scalidce present a constant facies, and are 

 easily recognizable by their salient ribs and continuous peristome, the 

 stud}'' of the Cretaceous and older fossil forms is beset with difficulties 

 on account of the forms met with which are transitional between Sca- 

 lidce and Chemnitzia, and also, though in a less degree, between 

 Turritella and Cerithium. It is an extremely rare occurrence to 

 find a specimen with the aperture perfect, and it will be seen that 

 only one of the species described has a circular mouth and complete 

 peristome. The borders of the peristome seem to have had a ten- 

 dency to disunite, and also present a weakening of the part applied 

 to the preceding whorl ; sometimes, indeed, every trace of border in 

 this region has disappeared, and the shell therefore loses the princi- 

 pal character which justifies its association with ScalidcB, the lips 

 being thin and the mouth oval, resembling Chemnitzia. Notwith- 

 standing, however, the differences in form of the mouth, the greater 

 number of these shells bear such a strong general resemblance to the 

 true Scalidce that they cannot but be placed in that family. It is as 

 well here to remark that there is some analogy between fragments of 

 Scalaria and Ai:>orrhais when the last whorl is not present; but the 

 direction of the ribs may be taken as a sort of guide, those of Scalaria 

 being nearly always parallel with the axis of enrolment, whilst in 

 Aporrha'is they are for the most part oblique. Of the thirteen genera 

 into which this family has been divided, two only are ajDparently 

 represented in the Cretaceous rocks of the British area, Scalaria and 

 Funis. ScalaricB proper, have been divided by d'Orbigny into two 

 groups : 1. Carinati, with an anterior keel transverse to the ribs ; 

 2. Pretiosi, without keel, and with uninterrupted ribs. The former 

 of these divisions is equivalent to Adams's sub-genus Opalia. 



In 1868 there were in all 45 species known, to which we are now 

 able to add several new forms, 



