80 BE. T. DAVIDSON ON EECENT BEACHIOPODA. 



Terebratella transversa, J. E. Whiteaves, Ou some Marine Invertebrata from the "West Coast of North 

 America, Canadian Naturalist, n. s. vol. viii. p. 468, 1878, and On some Marine Invertebrata from Queen 

 Charlotte Island, Keport Geol. Surv. Canada, 1878-79, p. 195 (1880). 



Shell very variable in shape, usually quadrispherically transverse, wider than long, 

 broadest posteriorly or near the hinge-line, which is very obtusely angular, almost straight, 

 very little shorter than the breadth of the shell ; marginal line flexuous and sinuated in 

 front. Dorsal valve moderately convex, channelled longitudinally along the middle by 

 a concave depression or sinus. Ventral valve much deeper than the dorsal one, with a 

 longitudinal elevation or fold extending from the beak to the front ; beak short, slightly 

 incurved, and truncated by a large incomplete foramen, margined anteriorly by a portion 

 of the umbo of the opposite valve, and laterally by two small deltidial plates ; beak- 

 ridges strongly defined, leaving between them and the hinge-line a flat or gently con- 

 cave smooth area. Surface of valves either smooth or more or less covered with faint 

 or strong angular ribs, here and there bifurcating, or with a short rib interpolated 

 between the larger ones. Shell-structure perforated by minute canals. In the interior 

 of the dorsal valve the hinge-plate is divided ; cardinal process small, and from under it 

 a mesial septum of small elevation extends to about half the length of the valve. Loop 

 long, doubly attached, first to the base of the hinge-plate, then to the anterior extremity 

 of the mesial septum by means of an oblique lamina given off from about the middle 

 of the length of the principal stems of the loop, when, after having attained their greatest 

 length, they become reflected in the shape of a loop. Colour varying from light ashy 

 yellow to a light or dark livid purple or red mixed with yellow, deeper in colour on the 

 lines of growth. Length 1 inch 3 lines, breadth 1 inch 7 lines, depth 10 lines. 



Hab. Off Vancouver Island, mouth of Cumshewa Harbour, in 20 fathoms; Houston- 

 Stewart Channel, in 15-20 fathoms (Whiteaves) ; Puget Sound to Sitka (Swan), Alaska 

 territory, peninsula of Aliaska ; Neeath Bay, from Aleutian Islands to Oregon (Dall) ; 

 coast of California at Monterey (Cooper and Dall) ; Catalina Island (Cooper). 



Obs. Dall justly observes, in his description of this species, in the ' American Journal 

 of Conchology ' for 1870, that " it presents every possible variation from longitudinally 

 oval to quadrispherically transverse, that many are unsymmetrical, and most of them 

 overgrown with Polyzoa, Serpulse, and Corallines." He also mentions that " some 

 specimens have from thirty to forty ribs or many fewer, and varying very much in 

 prominence; some have none at all, and others have theu* valves smooth and half 

 ribbed, some ribbed only on the umbones, others again near the margin." I have 

 detected all these modifications even in the limited number of specimens I have been 

 able to examine. 



To the completely smooth examples, Sowerby, in 1846, gave the name transversa ; to 

 a ribbed individual, Gould, in 1850, applied that of caurina (PL XVI. figs. 10-12), and, in 

 1871, Dall named a red variety, from the coast of California, Terebratella oceideiitalis. 

 Peeling somewhat uncertain with respect to the last-named species, I forwarded to Mr. Dall 

 a red specimen, of which I give figures (PI. XVI. figs. 13 & 11), and which agreed in every 

 detail, except in colour, with specimens from Sitka and Vancouver Island. In returning 



