CHAP. IV. VOLUTA - TYPES OF FORM. 115 



Analogies of the Types of VOLUTA to the ZOOPHAGOUS 

 Tribe. 



Genera Families 



p Qfthe Analogies. of the 



VOLUTINJS. Zoophaga. 



imperi..!.. 



Magnifica. Scaphella. Mantle very large. VOLUTIDJE. 



Angulata. Volutilithes. 

 Scapha. Harpula. { 



This table brings out two remarkable facts. The first 

 relates to the analogies of Valuta Scapha and of Har- 

 pula to the Strombidce all which, by placing these three 

 groups in separate columns, fall in precisely opposite to 

 each other. The second relates to the analogy between 

 the Muricida and the coronated volutes : these are all 

 the most spiny or muricated of all univalves. The 

 same principle of variation holds good between the 

 smooth melons and the typical Turbinellidce : both are 

 remarkably smooth shells ; both have very short papil- 

 lary spires ; and both have three or four well-defined 

 plaits on their pillar. But the sub-typical group of the 

 Turbinellidce are composed of those rough, spiny, and 

 often coronated shells, forming our genus Scolymus: 

 these, therefore, are analogous to the sub-typical genus 

 Cymbiola ; and, consequently, to all such forms or types 

 as represent them, as Voluta imperialis, Harpula hebrcea, 

 Volutilithes musicalis, &c. It seems to be one of the 

 laws of variation in the structure of the zoophagous 

 shells, that every one of the families* should contain 

 two prominent groups ; one remarkable for having 

 smooth, and the other rough, or spiny, shells. It 

 would even seem that Nature, so to speak, is so tena- 

 cious of this law, that she adheres to it in the very 

 smallest of her groups, that is, in the variations of sub- 

 genera. Among the most common instances, the reader 



* Except the Cyprceida, where it is obvious, from the little variation in 

 the shells, that the analogies must be traced from the animals only. 



