36 THE VOYAGE OF H.M.S. CHALLENGEE. 



exceptional specimens may be found in which the straight and indented front-line is 

 present, but is more often seen in the North Atlantic type. The young shells of both 

 seem undistinguishable. I have examined specimens from 1 mm. in length up to 27 mm. 

 Up to about 5 mm. and even more, the ribs are very few in number, prominent, 

 and radiate from the extremity of the beak to the margin, and are crossed by strongly 

 indented concentric lines which give the striae the so-termed tuberculated appearance 

 described by conchologists as well as by pala3ontologists, for the same character seems to 

 be prevalent not only in the recent species of the genus, but also in those that occur 

 fossil both in the Cretaceous and Tertiary formations. As the shell grows the ribs become 

 more delicate and more numerous from repeated interpolations of shorter ribs, and the 

 concentric lines become very much finer. The loop varies also considerably at difierent 

 stages of the shell's growth. When quite young it forms a simple semicircular curve 

 after having become attached to the hinge-plate, but as the shell grows the anterior 

 portion of the lamella is slightly bent upwards and the crural processes much so as in the 

 form of a ring. 



There seems to me to exist more varietal difference between the form of Terebratulina 

 caput-serpentis that occurs in the Mediterranean, and especially the North African coast 

 of that sea, than between Terebratulma caput-serpentis of the North Atlantic and the 

 North American variety septentrionalis. Dr Gwyn Jeffreys has proposed to me to apply 

 to the Mediterranean form the varietal designation of mediterranea. It is much more 

 depressed than the typical Terebratulina caput-serpentis, and often a strong longitudinal 

 depression or sinus is seen in both valves, and the front is usually deeply indented. In 

 the North Atlantic, Terebratulina caput-serpentis and American var. septentrionalis, the 

 dorsal valve is generally uniformly convex, and when a depression exists it is much less 

 defined than in the Mediterranean variety. 



Terehratulina caput-serpentis and its var. mediterranea are found fossil in the upper 

 tertiary deposits of many countries. 



Terehratulina, sp. (?) (PI. II. fig. 10). 



A single specimen of a Terebratulina, apparently closely aUied to Ter. caput-serpentis, 

 was also dredged by the Challenger Expedition on October 26, 1774, in lat. 7° 3' N., 

 long. 121° 48' E. of Mindanao, one of the Phihppine group of islands, in 82 fathoms. The 

 ribs are a little coarser, and the interspaces between them a little wider than in the larger 

 number of specimens of the variety septentrionalis, but from the inspection of a single half- 

 grown specimen it would not be safe to consider these details of sufficient importance to 

 warrant referring it to a separate species. I submitted the specimen to the inspection of 

 Mr DaU, who believes it to be specifically distinct from Ter. cap)iit-serp>entis and its 

 variety sep>tentrionalis. 



