1704 



THE VOYAGE OF H.M.S. CHALLENGER. 



teeth" and " aboral feet"; the teeth immediately surround the opening of the mouth, 

 whilst the feet are remote from it and usually placed in the aboral half of the body, 

 more rarely in the equator or in the oral half. The general form and structure are the 

 same in both groups of apophyses, but their position and direction is different ; the 

 circoral teeth are directed forwards, often parallel (at the base at least), while the aboral 

 feet are either divergent and directed backwards, or they diverge forwards in the basal 

 part, then form a large arch, and finally curve backwards. 



The number of the aboral feet, and their position relative to the circoral teeth, are 

 different but probably constant in each single species, and serve, in the first place, for the 

 distinction of genera and species. Tuscarora (in restricted sense) (PI. 100, figs. 1—6), 

 has constantly three feet (comparable to the three cortinar feet of the tripodal 

 Nassellaeia) ; Tuscarusa (PI. 100, fig. 7) has four feet, opposite in pairs and 

 forming a regular cross ; Tuscaridium, finally (PI. 100, fig. 8), has only one foot, 

 which is situated in the main axis, on its aboral pole, and may therefore be called a 

 caudal spine. 



The number of the circoral teeth varies from two to four, and is usually three. 

 Originally these three teeth alternate regularly with the three aboral feet, so that the 

 latter maybe regarded as perradial, the former as interradial (PL 100, figs. 1—4). The 

 proportion of the number of each group of apophyses in the different species is synopti- 

 cally shown in the following table : — 



The base of the apophyses in all Tuscarorida is inflated, conical, and pierced by a 

 small number of large ovate pores, the typical " basal pores," which occur also in the 

 closely allied Circoporida. The number of these basal pores varies from two to eight, 

 and is usually three or four ; it never becomes in this family so great as in the 

 Circoporida, where each circle of pores is often composed of sixteen to twenty -four or 

 more basal pores. The ntimber seems to be rather constant in each single species, as 

 may be seen in the preceding Table. The pedal pores (on the base of the aboral feet) are 

 usually larger than the dental pores (on the base of the circoral teeth). Their form is 



