134 POTAMIDES. 



Locality : Roti. 



This species has been collected by Dr. H. ten Kate. As 

 the appearance is the same as that of' Cerithidea Tenkatel 

 and the fragility of the shell is not in accordance with 

 its living in the sea, I suppose it may have been found 

 in the same salt lake as the Cerithidea ; moreover I received 

 a specimen , larger but not adult and slightly broken, from 

 that locality , for my private collection. 



In a specimen which I have broken to examine the ra- 

 dula , I found nothing of the internal laminae characteristic 

 for Terehralia ; however every other character refers it to 

 that subgenus. 



The only species to which this one might be ascribed 

 as a variety , is P. sulcatus Brug., but I fortunately have 

 received also from Mr. ten Kate a specimen from the same 

 locality, which belongs without doubt to that species; it 

 is rather small and thin , also blackish brown , but in other 

 respects agrees with the type , a. o. by the possession ot 

 the internal laminae, and the ribs are much less crowded 

 as in the var. costata of JP. tenerrimus. 



Moreover I have been able to examine the radula, which 

 differs in many respects, compared with the description 

 and figures of Troschel (Gebiss der Schnecken). 



The central tooth is not rounded but slightly emarginated 

 at the top; the opaque spot, near the base, if present at 

 all , is much less visible. However this may depend on the 

 conception of the drawer ; the cusps 3 in number are larger 

 (some teeth have 5 cusps). 



The lateral teeth have 4 instead of 3 cusps, the inner 

 margin of the base is less notched , the outer margin has 

 a small auricle, near the outer cusp. The first marginal 

 tooth is not so broad as in P. sulcatus, it has also one 

 denticle more , viz. 4 and has a small auricle at the external 

 side. The second marginal tooth has 5 cusps instead of 3 

 in P. sulcatus , of these the external one is the largest, as in 

 P. sulcatus ; this tooth has , like in the last named species a 

 large pellucid appendix on the external side , the margin 



Notes from the Leyden ^useuin, "Vol. XVI. 



