"""istHv"] PROCEEDINGS OF THE NATIONAL MUSEUM. 213 



tlie exterior scnlptnre, and the aperture is smooth and glossy. The 

 color iu one example is yellowish white, in the other the groundwork 

 is of said tint but apparently partially mottled with gray. Dimensions : 

 Altitude 3; latitude 4.25""". Altitude of mouth, 1.75; latitude 2.50'"™. 



Habitat. — West coast of Nicaragua. Two examples, iu the collec- 

 tion of the U. S. Nat. Museum (No. 101944). 



This peculiar and interesting form has in a very general way the 

 aspect of a tiny Stomatia phymotis and is probably parasitic iu its hab- 

 its like Thyca, or a domiciliare on some form like Echinus. The 

 Adams's subgenus Thyca is based on a shell that is "crystalline, 

 acutely conical, slightly curved, longitudinally grooved, parasitic on 

 starfishes." They include two species, aster icola, H. & A. Ad., and 

 cr ystallinHs Gouhl', which latter is a small nelcioushaped foim, with 

 the apex marginal and somewhat recurved, as in many of the Hippony- 

 cidce, which it, crystaUinus, judging by the figure in Gould's Atlas of 

 the Shells of the Exploring Expedition, resembles much more than 

 most examples of Pileopsis { = Ccq)ulus) to which the author referred it. 

 It can hardly be included in the Adams's narrowly restricted subgeneric 

 description. I have thought it better to make a new subgenus than to 

 expand that of Thyca, as it is not improbable that other forms will 

 sooner or later be brought to the knowledge of conchologists, that 

 would be naturally grouped with the s])ecie8 described above; perhaps 

 '■'• Fileopsis, Fig. 2381, ?P. BelessertiV^ Cheuu {vide Manuel de Conchy- 

 liologie, vol. i, p. 329), should be included in my subgenus, as judging 

 by the figure it is a true spiral shell. I have not been able to find any 

 description of Chenu's shell. 



Suborder Orthodonta. 



Superfamily RHACHIGLOSSA. 



Family Mitrid.e. 



Genus MITRA Lamarck. 



Snbgeuus Costellaria. Swaiusou. 



Mitra (? Costellaria) nodocaucellata, sp, nov. 



riate XV, Fig. 14. 



Shell small, dark brownish or dingy purple outside, dark blackish 

 purple, glazed in the mouth ; slender, rather obtusely elongated, can- 

 cellately sculptured throughout, except on the lower part of the basal 

 whorl near the aperture. Number of whorls five, slightly convex. The 

 three following the nuclear show three, the penultimate four and a par- 

 tial fifth, and the basal whorl nineteen to twenty prominent revolving 

 lira?; these are traversed by numerous equally prominent longitudinal 

 ribs, thus caucellating the surface quite equally, and forming at the 



