30 DE. T. DAVIDSON ON EECENT BEACHIOPODA. 



at present possess of the embryology, or early stages, of Terehratulina septentrionalis *. 

 This distinguished zoologist having dredged in 15 fathoms of water in the harbour of 

 Eastport, Maine, in 1869, individuals of all ages, has minutely and elaborately described 

 all the stages of its development, which he illustrates in the most complete and admirable 

 manner. The details and illustrations he communicates are so numerous that we feel 

 ourselves obliged to refer the reader to the author's memoir, and to limit ourselves to 

 the reproduction of the following selected observations and illustrations ; he says : — 

 "The species occur in great numbers, at various depths, and have also been collected 

 at low-tide mark, by Dr. Stimpson and Prof. Verrill. The specimens were found 

 attached to stones brought up in the dredge, and also adhering to the lower valve of 

 adult individuals, generally near the peduncle f The eggs were generally kidney- 

 shaped, though very irregular as to form and size [see Plate V. figs. 1-4] ; they 

 were spermaceti-white in color, and opaque, though having a central area, translucent, 



and apparently depressed This form recalled the general proportions of Argiope 



and Megerlia, in being transversely oval, in having the hinge margin wide and straight, 

 and in the presence of a proportionately wide foramen. This stage was exceedingly 

 minute, .... the shell showed nothing of the scale-like structure so characteristic 

 in later stages. Between this stage and the next, tlie shell rapidly elongates, while 

 the hinge margin remains nearly the same in width ; this is also shown in the concentric 

 lines of growth seen faintly on the surface, indicating a rapid increase in the length of 

 the shell, while no corresponding increase takes place in the widening of the hinge 

 margin. The peduncle is longer than the shell, having distinct walls apparently enclosing 

 a clear interspace, the end slightly dilating and forming a pear-shaped adhering disk. 



The structure of the shell showed clearly the scale-like structure, with the csecal tubules 



of the pallial lobes perforating it. The anterior margin of tlie pallial lobes gave rise to 

 seven setse of variable lengths, all of them projecting forward [Plate V. fig. 21]. . . . The 

 future position of the calcareous loop was indicated by a strongly arched process midway 

 the length of the shell, from which sprang six short and stout cirri, all of them curving 

 towards the mouth, which occupied the centre of the base from which the cirri sprang. 

 The digestive sac hung from the mouth, and was twice as long as broad, having a strong 

 constriction in the centre, forming two chambers, the lowermost one being globular in 

 shape, and having its walls colored a light reddish-brown, this colored portion evidently 

 indicating hepatic cells. The cavity next the mouth indicates the stomach, whilst the 

 lowermost cavity indicates the future intestine or cul-de-sac. The cirri moved fre- 

 quently, and in various directions, though generally performing a grasping motion, as if 



securing some bit of food In this stage, and several succeeding stages, the outline of 



the shell is remarkably like that of Lingula, and this resemblance is more striking from 

 the proportionally long peduncle. [Plate V. fig. 31.] 



" In another stage, the numerous irregular shaped calcareous spiculae lined the outer 



* " On the Early Stages of. Tcrehratulhia septentrionalis," Memoirs of the Boston Society of Natural History, 

 vol. ii. p. 29, 1871 ; and " Embryology of Terehratulina''' ibid. p. 249. 



t On an adult specimen of T. septentrionalis, dredged by the ' Challenger ' expedition, I counted no less than 

 twenty-eight young shells of the species attached to the surface of both valves, and more especially to its peduncle. — T. D. 



