282 PROCEEDINGS OF THE ACADEMY OF [1898. 



Genus HOLOSPIRA von Martens. 



This genus, which is confined to the mainland of Mexico and the 

 adjacent States of the Union, offers an interesting series of structures 

 in the internal lamella?, parallel to those of Urocoptis. The prin- 

 cipal divergence from that genus is in the frequent development of 

 parietal and basal lamella?, which are of rare occurrence in the 

 Antillean genera. 



Professor Dall, 9 who has ably investigated the subject, gives the 

 following classification, which seems worthy of unqualified ap- 

 proval : — 



Subgenus Holospira s. s., type N. pilocerei Pfr., with section 

 Bostrichocentrum Strebel & Pfeffer, Haplostemma, Eudistemma and 

 Distomospira Dall. 



Subgenus Metastoma Strebel & Pfeffer, type H. roemeri Pfr. 



Subgenus Ccelostemma Dall, type H. elizabethce Pilsbry. 



The first group includes species with an axial plait and usually 

 various other armature. More or less similar structures occur in 

 Gongylostoma. Metastoma has the axis simple, as in typical Urocop- 

 tis and Brachypodella. In Ccelostemma a swollen, vertically cost- 

 ulate axis is found, unlike any Antillean type, although there is 

 some analogy with the subgenus Idiostemma Pils. & Van. 



Genus EUCALODIUM Crosse & Fischer. 



In this Mexican genus the large, solid shell resembles typical Uro- 

 coptis; the axis is solid and sinuous, with a continuous spiral plait, 

 as in the subgenus Arangia P. & V., of Urocoptis. 



The subgenus Oligostylus Pils. 10 has the axis straight and smooth, 

 as in typical Urocoptis. 



These two types of pillar are exactly paralleled also in the genus 

 Macroceramus Gldg. and its subgenus Spiroceramus Pils. & Van. 



Subgenus Anisospira Strebel & Pfeffer. 



An eastern Mexican group, of few species. The soft anatomy is 

 still unknown. It seems to be a subgenus subordinate to Eucalo- 

 dium. 



Genus BERENDTIA Crosse & Fischer. 



Like Spartocentrum, to which it is closely allied ; but with the axis 

 solid, slender and smooth, and the spire tapering, with fewer, more 



9 Proc U. S. National Museum, xix, p. 344, 1896. 



10 See Dall, The Nautilus IX, p. 51 ; Proc. U. S. Nat. Mus. XIX, p. 348. 



