ADDITIONS TO "BRITISH CONCHOLOGY. 



(Continued from page 171). 



By J. T. MARSHALL. 



Odostomia (continued). 

 Sometimes, it may be. the artist has not caught the same aspect of the 

 shell as the writer, and this itself might result in a considerable diver- 

 gence from the type form. Only in this way can I account for some 

 authors' figures differing so much from their written descriptions, 

 instances of which will be pointed out in the following pages. Type 

 forms, especially of such minute and uncharacteristic shells as the 

 Odosiomice, should be taken by photo-lithography, and in variable 

 species several figures should be given to show the range of variation. 

 The working out of this extensive and interesting group I can 

 recommend as a good mental exercise. I have studied it more or 

 less for nearly forty years, and my mounted specimens do not number 

 less than 20,000, collected from all parts of the British Isles and at all 

 depths. Some of the species I have fully dealt with in previous papers. 

 I do not profess that my notes thereon are more than an elucidation 

 or confirmation of previous writers, nor that it contains much original 

 matter, Jeffreys having left very little original work for gleaners on a 

 subject in which he vols, facile princeps, and which he had made almost 

 entirely his own. But I think it will be found that my records have 

 considerably increased the area of distribution in the British seas 

 of most of our species and varieties. 



The following short characteristics of the more critical Odostomm 

 will be found useful: — 



O. minima. — Like a young O. nitidissima. 



O. nivosa.— Cylindrical; spiral stria; round periphery. 



O. truncatula. — Like a large O. nivosa; spiral stria; throughout. 



O. clavula, — Short, tubular. 



O. lukisi. — Like a stunted O. conoidea with rounded base. 



O. albella. — A long oval; slight umbilicus and tooth; thin. 



O. rissdides. — Rounded whorls; rounded mouth; umbilicus and 

 tooth slight. 



O. pallida. — Short spire; long body-whorl; no umbilicus; solid. 



O. conoidea. — Grooved mouth ; flattened whorls ; keeled base. 



O. acuta. — Conical; funnel-shaped umbilicus. 



O. umbilicaris. — Like a stumpy O. acuta. 



O. unidentata. — Like O. acuta, but no umbilicus; squarish base. 



O. conspicua. — Like a large O. unidentata, with deeper suture. 



O. turrita. — Like a dwarf O. unidentata, with narrow base. 



0. plicata. — Long and slender; whorls compressed, 



