42 Transactions. 



the shell from the posterior margin. The surface of the valve is orna- 

 mented by fine radial ribs, which are obsolete, or may never have been 

 developed, near the apex, and are crossed by ii*regiilarly developed growth- 

 lines. The shell is thick and solid in the older specimens, and the fine 

 punctuation can be seen in the interior by means of a lens. The colour 

 varies from light brown to almost colourless. 



In the interior of the dorsal valve there- is a narrow margin encircling 

 the valve, separated from the rest of the interior by a rounded shoulder, 

 and not granulated. The musc^ilar impressions are white and porcellanous. 

 and afiord an easy means of distinguishing the species from the molluscan 

 limpets. The posterior adductor-scars are large, nearly round, and situated 

 near the posterior angles of the shell. The unpaired (posterior) muscle has 

 left practically no impression in any of the specimens. The anterior 

 adductor-scars are smaller than those of the posterior adductors, are 

 crescentic in shape with the convex sides directed posteriorly inwards, and 

 approach one another on their inner ends. On their concave sides there 

 are well-marked depressions in the floor of the valve. The impressions 

 of th.e dorsal protractors lie close to the outer and hinder sides of the 

 posterior adductor-scars, and are small and oval in shape. The impressions 

 of the retractors of the arms lie close to the (juter ends of the anterior 

 adductor-scars, and are small and rounded in shape. The protractors of 

 the arms have left a single minute impression situated mesially in front of 

 the anterior adductors, and from it a well-marked groove extends nearly 

 to the front margin. This groove appears to be one of the pallial-sinus 

 impressions, and on each side of it lie four similar grooves of irregular 

 length. 



The dimensions of the holotype are : Length, 12 mm. ; breadth, 11 mm. ; 

 height of dorsal valve, 4-5 mm. 



C huttoni differs from most living species of Crania by the absence of 

 a granulated rim in the interior of the dorsal valve, and in this respect, as 

 well as in shape, agrees with Crania japonica Adams. From this species, 

 however, it is easily distinguished by the radiating ornament as well as 

 by internal characters. The only other Recent species with radiating 

 ornament is the Australian Crania suessi Reeve, which is described as .sub- 

 orbicular, and therefore differs in shape. The genus is not yet known 

 fossil in the Tertiary of the Southern Hemisphere. 



(2.) On the Generic Position of the Tertiary Terebratulids of the 



Southern Hemisphere. 



The correct generic assignment of the New Zealand, Australian, and 

 Western Antarctic Tertiary fossils formerly known as species of Terebraticla 

 is a matter of no little difficulty in view of the close restriction of that 

 genus by Buckman (1907). Terebratula terebratula, the genotype, is a bi- 

 plicate Pliocene shell from Italy, and only those species in actual genetic 

 connection with it may be admitted to the genus. The biplicate Cre- 

 taceous and Jurassic species may be excluded easily enough, since the 

 great difference in time is alone sufficient to prove that these species have 

 attained biplication from different ancestral forms ; but a difficulty arises 

 in connection with the uniplicate and biplicate older and middle Tertiary 

 species, for there is no a priori reason why these should not be in actual 

 genetic connection with Terebratula terebratula. Some of them, however, 

 must belong to Liothyrina, which is believed to have existed since the 



