of the North Atlantic and of North-Western Europe. 669 



The exact locality is unknown to us. The specimens were dredged by 

 the " Talisman," July 11, 1883, in 932 mfetres, and received by us from tbe 

 Marquis de Folin ; the date would lead us to suppose that T. ctenorhynchus was 

 taken off the coast of Morocco. 



The shell, in this species, is quite different in form from any other species 

 which is as yet known ; and very marked characters are present in the animal in 

 the peculiar form of the aj)pendicular branch of the antennae ; in the character of 

 the "masticating" process of the mandible, in the remarkable large tooth of the 

 second maxillse, and the reduction in size of the other part of that limb ; in the 

 very rudimentary character of the vibratory lamina of the penultimate limbs, and 

 in the spination of the ungues of the cauda, these ungues are sometimes ciliated, 

 sometimes crenated, sometimes minutely denticulated, or serrated, but in no other 

 case do we know them so strongly spined as in this species. 



2. Tetragonodon erinaceus, n. sp. 



(Plate Lix., figs. 14, 15.) 



' Shell, seen from the side, doubly bent, in general form ovate, with the 

 anterior rostrate portion obliquely directed downwards, and the posterior sub- 

 central triangular jjrojection bent slightly upwards; ventral margin regularly and 

 evenly arched throughout, in front penetrating at the antennal sinus to nearly 

 half the entire height of the valves, thence the rostrate process is directed obliquely 

 forwards and downwards to a remarkable length, with the extremity narrow ; the 

 antennal sinus is very widely open ; the dorsal margin is anteriorly gently arched 

 to the extremity of the rostrate process, centrally it is nearly straight, posteriorly 

 the declination is sudden but well rounded ; tlie posterior extremity is produced 

 into a triangular compressed process, of which the upper side is nearly perpendic- 

 ular to the hinder margin, while the lower is a portion of the continued sweep of 

 the ventral margin. The total length is somewhat less than twice the greatest 

 height, and the greatest breadth is equal to five-sixths of the height. The valves 

 have a nearly perpendicular depression across them slightly behind the middle, 

 and their entire surface, except the extremity of the posterior triangular projection, 

 is covered with spinous processes, which for the most part are acute at their 

 termination, but in some cases, especiall}'- on the hinder ventral portion of the 

 valves, these spinous processes have clavate terminations. Viewed from above 

 the form is ovate, the sides arched, the great anterior rostrate process projected 

 in almost sub-quadrangular form, and the posterior triangular process appearing 

 as a small rostrate projection. Length, 2 mm. ; height, 1"1 mm. 



Off Cape Blanco, coast of Morocco, "Talisman" Expedition (Marquis de Folin). 



lEANS. ROT. DUB. SOC, N.S. VOL. V., PAETXII. 5B 



