LECTURES ON MOLLUSCA. 193 



The known species in this family amount to at least five hundred. 

 First appearing in the later cretaceous age, they very rapidly became 

 plentiful in the tertiary strata, three hundred species having been 

 already described. But although so plentiful in forms, they are gen- 

 erally, like the Pyramidellidce, rare in individuals ; and collections may 

 often be seen entirely destitute of them. They are generally found in 

 deep water, ranging however from low water to a hundred fathoms ; 

 and culminate in the China seas and in west tropical America. 



Family Terebrid,e. (Augur-shells.) 



The Augur-shells form an aberrant family, in general easily recog- 

 nized by the very slender and produced spire, with flattened whirls and 

 a deeply-notched aperture. Although several of the species are toler- 

 ably large, and very common in the Pacific islands, their anatomy is 

 as yet but little known. This group, like the other Toxifers, has only 

 appeared late in the history of our planet. About thirty species have 

 been found in the tertiaries ; but in the existing seas, fully two hun- 

 dred species have been discovered. They live in deep water, almost 

 always in tropical climates. So far as known, the teeth and proboscis 

 are like those of other Toxifers, but the foot and head of the animal are 

 very small. The tentacles are close to the mouth, exceedingly minute, 

 and with mere sjjecks of eyes at their summits. Sometimes the eyes 

 and even the tentacles are not to be seen ; and the head is little more 

 than a mouth, as in the shell-bearing Pteropods. The nose-pipe how- 

 ever is very long, and reflected through the sharp notch. The intro- 

 mittent organ is longer still, like a living thread proceeding from the 

 nape of the neck. There is a small, horny operculum, not filling the 

 mouth, and shaped somewhat as in Pleurotoma. The shells are gen- 

 erally glossy, heavy, and prettily painted and sculptured. The upper 

 whirls of the shell are often of chalcedonic texture, the inner cavity 

 having been filled up with glossy shelly matter. In this respect there 

 is a striking contrast between the Augurs and the Screws, which latter 

 group partition off the upper whirls with thin septa. The Screw-shells 

 therefore are often found broken ; while the Augurs are generally per- 

 fect. The Augurs are so slender that sometimes as many as thirty 

 whirls may be counted on a shell three inches long but not a quarter 

 of an inch across at the broadest part. It can hardly be believed that 

 the creature can balance his heavy pole, crawling like an ordinary Gas- 

 teropod, and supporting his weight on so short a foot at an enormous 

 leverage against him. It is not improbable that he lives in the midst 

 of sandy mud, through which he can easily push his needle and twist 

 round ; leaving the top of his long nose in the water. In such an 

 abode, eyes would be of no service. 



It is not yet known how far the differences in the shells are coordi- 

 nate with those in the animals. Dr. Gray divides the family into 

 those with, and those without tentacles and eyes. From the former 

 he separates a genus Leiodomus, in which the suture is callous, like 

 Bullla; but the foot is small, not bulky, as in that group. For the 

 present, it is convenient to separate the non-sculptured species as 

 Subula; keeping Terebra for those with a band near the suture. The 

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