40 THE VOYAGE OF H.M.S. CHALLENGER. 



broad ; as seen from without, one half is open leading into the interior, the other is closed 

 by the very curved septum. Margin crenulated and crimped by the ribs. Inside glassy, 

 blunt at the top, not being hollowed into the apex, strongly furrowed by the ribs, less so 

 by the concentric threads ; there is no anterior furrow : seen from within, the slit is semi- 

 oval, and the strong septum is excessively short and straight and is almost perpendicular ; 

 from it a slight callus encircles the opening of the slit. L. 0"25 in. B. 0'16. H. 0'13. 



This species in form somewhat resembles Puncturella agger, but is longer and narrower ; the 

 sculpture and slit are very markedly, and the apex at least unmistakably, different. In all these 

 respects it differs from Puncturella noachina, Linn., to the young of which it has a vague resemblance. 

 That species also is usually in all stages of growth narrower in front than behind I failed to recog- 

 nise either the white or transparent specks, one or other of which are so generally present in the 

 Fissurellidas. 



2. Puncturella agger, 1 Watson (PL IV. fig. 6). 



Puncturella agger, Watson, Prelim. Report, pt. 16, Journ. Linn. Soc. Lond., vol. xvii. p. 32, sp. 3. 



Station 24. March 25, 1863. Lat. 18° 38' 30" N., long. 65° 5' 30" W. N. of Culebra 

 Island, West Indies. 390 fathoms. Pteropod ooze. 



Shell. — Small, porcellanous, oval, broader in front ; side slopes straight, the front 

 convex, the back concave, rather high, but with the top depressed and thrust out back- 

 wards, yet little projecting, the apex being flattened out on the posterior slope; there are 

 many not crowded slight radiating ribs set with stumpy prickles ; the long and lanceolate 

 slit is on the crest, and from it a ridge runs down the front slope. Sculpture : The riblets 

 are very slight, but are made distinct by the little triangular prickles which pretty closely 

 stud them ; these prickles more irregularly and remotely tally with feeble lines of 

 growth ; the ridge down the front slope is small, and is crowned with two of the riblets 

 parted by a narrow furrow ; these riblets along the slit rise into sharp laminse. Colour : 

 The shell is porcellanous white, with a slight ruddy tinge. Apex somewhat depressed 

 and shortly projected backward, curling in on the central line of the shell, but with the 

 extreme tip flattened out on the posterior right slope. There are 2^ whorls in all. Slit 

 lies high on the front slope, distant from the apex about once, and from the margin about 

 twice its own length. It is long and narrow, bluntly rounded at the upper end, and 

 produced in front to a long sharp point. Margin is thin and not fretted with the rib- 

 ends. Inside glassy, deeply hollowed into the apex, feebly rayed, and having the rays 

 picked out with bright specks corresponding to the external prickles : a long shallow 

 furrow, bordered by a minute ridge on either side, runs widening upwards from the margin 



1 So called from the little ridge that runs down from the front slope of the shell from the slit. 



