INSTITUTE OF SCIENCE, PHILADELPHIA. 443 



Genus CADULUS Philippi. 

 Cadulus Philippi, En. Moll. Sic. ii. p. 209, 184:). Type C. ovulum Ph. 

 Gadila Gray, P. Z. S. 1S47, p. 159. 

 Gadus Rang, Deshayes, non Linn^. 

 Helonyx Stinipson, Am. Journ. Conch, i. p. 63, 1865. 

 Dischides ]e(i{e.)!S, Ann. Mag. Nat. Hist. 1867, xx. p. 251. 



Since Caduhts is the oldest name, it must take precedence of later ones 

 which represent merely minor divisions of the genus of which Cadjibis is the 

 type. That is to say, if Pnlselbivi and Cadiihis are to form portions of a single 

 genus, this genus must be called Cadiihcs, and the other name, which dates 

 only from 1868, must be regarded as a subgenus or section of Cad^dus. This 

 very obvious rule has not been observed as consistently as could be wished, 

 though a little reflection will show that it must be regarded as necessary. 



It is impossible to discriminate, in dealing with fossil species, between 

 those belonging to Cadidtis proper and Siphonodentalunn. The anal orifice of 

 the shell may be waved or simple on its margin in different specimens of the 

 same species, while those which have the margin cut by several slits or notches 

 exhibit considerable variation in the details, as has already been shown by 

 Fischer. The forms treated of here will therefore be referred to Cadjdits, 

 though it is by no means improbable that more than one genus is represented 

 among them. The posterior orifice, as far as I have been able to judge from 

 material in different stages of growth, is always circular at first; as the shell 

 grows, in many species, it becomes dorso-ventrally somewhat compressed, and 

 if there are to be sulci in the posterior margin they appear, being first shallow 

 waves and gradually deepening by absorption intp slits in those species which 

 have slits. Some stop in the first stage, others in the second, others proceed 

 to the third. If the slits are deep and wide, the little points of shell between 

 them are very easily broken off, and thus it frequently happens that the aper- 

 ture is reduced to its original simplicity. Then the process of producing the 

 sulci begins again, and so the cycle repeats itself. As the tube grows, it reaches 

 a point where the cingulum or greatest equatorial diameter is secreted, from 

 which it diminishes to the anterior orifice. The section of the cingulum is 

 usually, but not invariably, circular, even in species which are compressed 

 behind and before the equator; the completed aperture is often circular while 

 the shell a little way behind it is tnore or less compressed. Or the aperture, 

 from being oblique to the axis, may appear circular when a straight section 

 would result in an oval outline. 



Altogether, it will be observed that the description and estimation of 

 species in this group — especially among fossils, where perfect preservation and 

 large numbers of specimens may not be had for the asking — are beset with 

 difficulties, and in the present instance the writer is by no means confident that 

 he has reached in all cases a correct conclusion, notwithstanding his best efforts 

 in that direction. It is also: uncertain, as yet, whether mere size is a specific 



