AMERICAN JOURNAL 



OBSERVATION'S ON PLEIODON MACMURTRH, 



BY T. A. CONRAD. 



In the monograph of this genus in Reeve's Conchologia Iconica^ 

 this species is confounded with Swainson's P. ovatus. It is, there- 

 fore, I think, possible that a specimen of my species has never 

 yet reached Europe, and none but the typical specimen has, to 

 my knowledge, been brought to this country. I will therefore 

 indicate the differences between the two species, and I am con- 

 fident time will prove them to be distinct. The present shell is 

 lighter, more ventricose, shorter or higher, with a more promi- 

 nent summit and ventricose umbo, and is more obtuse posteriorly ; 

 within, the hinge differs in being narrower under the apex, and 

 the teeth more regular except at the posterior end of the cardi- 

 nal line. These teeth are very much compressed single and 

 acute, Avhilst in the ovatus they incline more to be double ; the 

 posterior cicatrix is separate, even distant from the impression 

 above it, but in the ovatus these scars are broadly confluent. 

 Another distinctive mark is the anterior end of the cardinal line^. 

 which suddenly becomes much contracted over the cicatrix 

 and is toothed finely nearly to the cardinal extremity. In all 

 the specimens of ovatus that I have seen the cavity of the umbo 

 is deeply tinged with dark green over a wide space, but in the 

 allied species this part of the interior is pure rosaceous, and the 

 only green is a bright spot under the anterior hinge margin, a 

 dull larger stain beneath it, and another small stain near the 

 posterior ventral margin. 



