1915.] NATURAL SCIENCES OF PHILADELPHIA. 335 



almost every form known l^y large lots) may be (1) Superior, axial 

 and basal, or (2) axial only. In Hachita forms we have also the 

 combination (3) axial and basal, which is never found in the Chirica- 

 huan series, where it is replaced by the combination (4) superior 

 and axial. Every Hachita species has, therefore, in different speci- 

 mens of the same colony, the characters of the supposed subgenera 

 or sections Bostrichocentrum, Haplostemma, Distomospira, and Tri- 

 stemma, while a Chiricahuan species will belong to Bostrichocentrum , 

 Eudistemma, and Tristemma. In external form and sculpture there 

 are no differences greater than specific between the Hachita and 

 Chiricahua species. 



The Hachita Holospiras belong, if we accept the criterion of 

 intergradation, to only one species, for which the prior name is 

 H. crossei. Between this species and H. bilamellata there is a perfect 

 series of intergrades in size, sculpture and number of whorls. We 

 mean by this that some individuals of an H. crossei colony could not 

 be distinguished from mearnsi; some mearnsi can be exactly matched 

 in a colony of hilamellaia, or of media; and certain slender shells of 

 bilamellata would pass as longa. The other named forms are more 

 distinct, probably because we did not happen to collect where th e 

 intergrading colonies live. The races are therefore based upon the 

 forms dominant in each colony. One might easily define a half 

 dozen species, if only a few shells from each place were in hand; 

 or if the internal lamellse were taken to be of specific weight, it 

 might be thought that there are between two and three times that 

 number. 



There are many colonies, most of which have some special char- 

 acters. A thorough exploration of the northern end of the range 

 will undoubtedly bring to light very many more forms, so that any 

 treatment of the group must now be tentative. For our present 

 purpose we consider the smallest form (crossei) and the largest (bi- 

 lamellata) as species, ranking the others as subspecies, though in some 

 cases they are more distinct than these two are from one another. 

 Several thousand shells were collected. 



The colonies at Stations 1, 2, 3, 12, are of very limited extent, 

 physical features restricting them. Station 5 is much larger. The 

 other Stations, 4, 6, 8, 9, 10, 11, merely represent collecting points 

 in large areas where Holospira may be picked up almost anywhere 

 over considerable tracts, while at the same time there are large 

 areas in the region over which these stations are scattered where 

 no shells can be found. 



