10 ON SOME TERTIARY FOSSILS, 



lines being very neat, distinct, equal, and sufficiently distant to 

 leave very definite rhomboidal spaces. The whorls are keeled 

 in the middle, about which there is a rather broad, fiat, shallow, 

 groove which corresponds to the sinus. It has a fine' line in the 

 centre, and is closely transversely marked with elegant curved 

 ribs. The aperture is wide, the labruin much produced in the 

 middle, and the sinus is very conspicuous, wide and deep. The 

 canal is twisted. The neat distant cancellation, and the 

 fine lines on the groove give the surface an appearance of open 

 thread work, hence the name. 



Pleurotoma rhomboidalis. PL 2, fig. 9. 

 Testa ' parva, rlwmboidea, tenui, nitente, a/pice obtuso ; anfr. 4£, 

 ultimo longe majori, superne obtuse angulato et oblique, undulose, crebre 

 eleganterque costato, spiraliter tenue lirato ; infra spiral iter, distanter 

 carinato ; supra angnlum late sulcato; sutura anguste canaliculata et 

 eleganter coronata ; nucleo conspicuo, tumido, Icevi ; spira cancellata ; 

 apertura anguste ovata, postice acuta, labro tenui, acuto, labio definito, 

 canali lato, aperto,parum elongato ; sinu lato, prof undo, supra unguium 

 sito. Long. 5, lat. 2^. 



This small shell of which I have only seen one specimen, is 

 described from what is evidently a young individual, but 

 sufficiently developed to determine its character. Shape rhom- 

 boidal and almost like a Conns. The lower part of the last whorl 

 is spirally distantly keeled with small rounded inconpicuous keels, 

 and crossed lengthwise with conspicuous irregular undulating 

 lines of growth. Last whorl obtusely angled above, at the line of 

 sinus, where it is ornamented with crescentic, small, close, neat 

 ribs, making a very handsome coronate ornamentation. Above 

 this there is a groove, and then a beautifidly coronate margin to 

 the suture, which is channelled. The whole of this part of the 

 shell is cancellated by close round liroe ; the nucleus is pullus- 

 like and smooth. Aperture acutely angular posteriorly. Canal 

 not very long and rather broad. 



