ACROURA. 



153 



incurved (fig. 5 b) ; the lateral scuta support a number of small scales instead of spines, 

 as in other genera. 



AcROURA Brodiki, Wright, n. sp. PI. XVII, fig. 5, a, h, c. 



Disk very small, indistinct ; rays long, very delicate, slightly tapering, nearly a 

 uniform thickness throughout, six times the length of the diameter of the disc ; lateral 

 scutae with scale-like appendages. 



Dimensions. — Diameter of the disk one eighth of an inch ; length of the arms eight 

 tenths of an inch. 



Description. — It is with considerable doubt that I have referred to the genus 

 Acroura this small OpJiiura, discovered by my friend the Rev. P. B. Brodie, F.G.S., in the 

 Middle Lias near Cheltenham. Its place there I consider only as provisional until the dis- 

 covery of better specimens enables us to understand its structure. 'Wq disk is extremely 

 small and indistinct ; the rays are long, very delicate, and taper slightly, being nearly of 

 a uniform thickness throughout ; the osselets are nearly twice as long as ihey are broad, and 

 the dorsal plates are deeper than wide, the few lateral plates that are preserved show small 

 scale-hke appendages (fig. 5 c). The length of the osselets, and the small scales on the 

 lateral scutes, have induced me to place it in the genus Acroura. Under the microscope, 

 armed with an inch-object-glass, the plates appear to be covered with fine transverse 

 lines of ornamentation. 



Affinities and Differences. — The sniallness of the disk, and the proportionate length 

 of arms, six times as long as the diameter of the body, readily distinguish this species 

 from Ophioderma tenuibrnchiata, the only species of the Middle Lias for which it could be 

 mistaken ; the extreme delicacy of the rays, and their nearly uniform diameter throughout, 

 with the length of the osselets, form good characters for its diagnosis. 



Locality and StatigrapMcal Position. — This Ophiura was collected by my friend the 

 Rev. P. B. Brodie, from the Middle Lias of Hewletts Hill, near Cheltenham, in the zone 

 of Ammonites capricornus, during the excavation of that rock for one of the reservoii^s of 

 the Water-company of that town ; it was associated with the stem and side arms of 

 Fentacrimis robustus, Wr. I dedicate this species to my friend the Rev. P. B. Brodie, 

 P.G.S., who has kindly communicated for this work the only specimen found. 



