CONTRIBUTIONS TO PALiEONTOLOGY. 59 



Rhynchospira ; while at the same time taking the direction of Trema- 

 TOSPIRA, it must exclude all those of the type of R. serpentina, which 

 would thus be left without a generic designation, and which in that event 

 I would propose to name Eumetria. 



The preceding remarks upon the Genus Retzia have been made 

 more with the intention of calling the attention of palaeontologists 

 to the characteristics observed in several species, than of finally 

 determining the question of generic relations among the several 

 groups. The European material in my possession is quite insuffi- 

 cient to furnish satisfactory illustrations of all the parts which, 

 are desirable for comparison. My specimens of the type of R. 

 serpentina have furnished no separate valves, and the little I have 

 shown has been derived from very unpromising material. These 

 species (and perhaps others of the same type) occurring in con- 

 siderable numbers in the Carboniferous limestones of the Missis- 

 sippi valley, will doubtless furnish to western collectors the means 

 of determining the entire characters of this group. 



NOTE ON THE GENUS LEPTOCCELIA. 



Among the specimens sent to me by Dr. Rominger, are two in- 

 dividuals of LeptoccoJia concava, showing the existence of internal 

 spires ; and a careful examination of my own collections from the 

 Lower Helderberg group has shown several specimens possessing 

 these internal organs which have their apices directed obliquely 

 outwards, and are connected near their origin by a strong vincu- 

 lum on the dorsal side. After repeated examinations of a large 

 number of the Oriskany sandstone species, from which the cha- 

 racters of the genus were mainly drawn, I have failed to detect 

 internal spires. The form of the internal loop, as represented in 

 the figures of the genus, was ascertained, as stated by me, mainly 

 from cavities remaining in the crystalline filling of the shell. 

 There were no appearances of spires ; nor does a re-examination 

 of the specimen afford any farther information, or indicate in any 

 manner that spires have ever existed. The crura can be traced to 

 the division at the process, and below this is a flat cavity. 



A critical re-examination of the fossils referred to this genus 

 shows that there are at least three distinct types, in their external 

 form and features, which, in the absence of positive knowledge 

 of the internal structure, were grouped together. A farther exa- 

 mination shows some peculiarities of hinge-structure in each one 



