110 Prof. W. King on Agulhasia Davidsonii, 



reflexed, and attached to the hinge by two cnu'a. Shell-sub- 

 stance penetrated by branching tubuli. 



This genus is singularly interesting in being the only one 

 of the Terebratulidajj and, with few exceptions, the only one 

 among the Ancylobrachs*, that has the beak pointed, and its 

 point non-foraminate. In these respects, however, it re- 

 sembles the Helictobrachiate genera Rhynchonella, Spirifer^ 

 &c. With the latter it agrees in having a subapical foramen ; 

 but it is distinguished from them by the absence of an external 

 plate (divided, or midivided) closing the deltidium. It is tiaie 

 this opening is closed by an internal plate : I consider the latter 

 part, however, to be the homologue of the internal arch, attached 

 to the inner surface of the area, common in Spiriferids, as 

 pointed out in my "Monograph of Syringothyris cusjjidafus^^'f. 

 No Ancylobrach, as far as is known to me, possesses any such 

 appendage. A further agreement between AyuJhasia and many 

 Spiriferids offers itself in the foramen being situated at the car- 

 dinal tennination of the deltidium. In possessing an area the 

 new genus resembles Trigonosemus, Ismenia^ Fissurostra, and 

 some other Ancylobrachs ; but in these genera the foramen is 

 situated at the apex of the beak, and the deltidium is usually 

 closed by the ordinary external plate. 



Histologically, Agulhasia departs from most of the Terebra- 

 tulidffi in having the singular branching tubulation w^hicli, as 

 I have elsewhere made known, characterizes Terehratulina 

 cajnit-serpentis J . 



From the difficulty in examining the microscopic shell- 

 structure of Mr. Davidson's specimens without breaking them, 

 I am unable to say that the tubuli are so numerously and 

 strikingly subdivided as those of the species in which they 

 first occurred to me, though there is some appearance of a 

 close approximation to it. 



• I am unacquainted with any other Ancylobrach, except the genus 

 Strivyocephalus, that has not the beak truncated by a foramen. 



t See Ann. & Mag. Nat. Hist. July 18G8. 



X See " Histology of the Test of the Class Palliobranchiata," in Trans- 

 actions of the Royal Irish Academy, vol. xxiv. part xi. 18(50. Fig. 8, 

 PL XI., is a copy of a figure in this memoir, representing the branching 

 tubuli of TerehraUiUna caput-serpe/itis. Their agi-eemeut in histological 

 structure suggests a genetic relation between Agulhasia and Terehratulina ; 

 but the areal and apophysial features respectively characterizing these 

 genera do not seem to lend much favour to this view. I have some 

 grounds, however, for suspecting that, different as they are, there is a 

 closer relation between them than would at first sight be admitted. Mv 

 investigations with reference to this question are not yet completed ; so at 

 present I can do no more tlian merely give expression to a suspicion, which 

 may or may not be hereafter confirmed. 



