MUSEUM OF COMPARATIVE ZOOLOGY. 236. 
When dredged, the washed contents of the trawl may present several 
bodies looking like wads of fine flax soaked in mud, and having various dead 
shells or worm-tubes entangled therein. In this unpromising nidus is hidden 
our gem of the sea. Long continued gentle washing under a stream from the 
water-cock finally removes most of the mud. Immersed in water, we see that 
the nest is composed of the finest and most silky threads, inextricably inter- 
laced and of great strength. Among them the young nestle until they are 
ready to spin for themselves. Many of the threads centre at and are con- 
nected with the byssal sinus, from which much force is necessary to detach 
them. 
It will be seen from the notes on the soft parts that this mollusk is most 
nearly related to Modiola, and not to Modiolaria, as before examination I sus- 
pected. I have compared it with the chief types, and there is no doubt of this. 
If we separate the polished species from the bearded mussels, this species, ac- 
cording to Fischer, may be referred to Amygdalum Megerle (1811), from which 
it hardly differs. Monterosato proposed the name Modiella for it ; but this 
had been used a year earlier by James Hall (1883) for a different group. 
Modiola opifex Say. 
Modiola opifex Say, Journ. Acad. Nat. Sci. Phil., IV. p. 369, pl. xix. figs. 2, 2a, 2b, 
1825; Phil. Abbild. und Beschr. n. Conchyl., III. Modiola, p. 21, t. ii. fig. 7. 
One valve was dredged from 640 fms, in Yucatan Strait, a depth which it 
doubtless reached in some accidental manner. This species was described by 
Say as attached to Pecten nodosus, and found in a mass of sand grains of its 
own collecting. Kroyer had it from Brazil, and the U.S. Fish Commission 
has dredged it to within a few miles of Cape Hatteras, but only as separated 
valves. It forms a transition, conchologically, between Modiolaria and the 
group typified by Modiola semen, sometimes called Botula. 
Genus CRENELLA Brown. 
Crenella decussata Monraeu. 
Crenella decussata Montagu, Dall, Bull. M. C. Z., IX. p. 116. 
Nuculocardia divaricata D’Orbigny, II. p. 311, pl. xxvii. figs. 56-59, 1845. 
Habitat. Barbados, 100 fms. (Alaska, California, New England, British 
seas, Norway, etc.). 
This little shell is proportionately a little more solid and strong than north- 
ern specimens, and the crenulations which exist in both, and from which the 
group takes its name, partake of this difference. I have seen nothing, how- 
ever, in the few specimens I have been able to examine, which would authorize 
the separation of the southern form from the northern one. 
