540 MOLLUSCA. 
1. Mycetopus subsinuatus. (Tab. XLI. figg. 5, 5a.) 
Mycetopus subsinuatus, Sowerby, in Reeve’s Conch. Icon. xvi., Mycetopus, t. 4. fig. 10 (1868) ’. 
Shell pod-shaped, in the hinder part higher, narrowed before, rounded at the fore extremity; dorsal margin 
ascending in a straight line posteriorly, forming an obtuse angle at the hinder end of the ligament 
in five-sevenths of the whole length, thence descending obliquely to the hinder extremity, which is more 
rounded than angulated ; ventral margin gaping and slightly sinuated in its anterior half, moderately 
convex in the hinder half. Periostracum greenish-yellow. Summits in scarcely one-fourth of the whole 
length, not prominent, decorticated. Sinulus longer than deep, with a downwardly directed point nearer 
its anterior end. Inside whitish, somewhat dull. 
a. Long. 132; alt. vert. 324, ale 43, diam. 23 millim. 
b=, =: 125; » 34, , 45, 4, 23 4, 
c« 4 118; ” 30, , 42, 4» ? » 
a, 6. Guatemalan specimens collected by Stoll; c. Sowerby’s type from Bogota. 
Hab. W. Guatemata: Paso Antonio, in the Pacific coast region (Stol¢). 
CoLoMBIA: Bogotal?. 
I figure one of Stoll’s specimens in order to show its close resemblance to Sowerby’s 
figure. 
2. Mycetopus weddelli. 
Mycetopus weddelli, Hupé, in Castelnau’s Anim. nouv. ou rares de Amérique du sud, Mollusques, 
p- 93, t. 20. fig. 2’; Tate, Am. Journ. of Conch. v. p. 160 (1870) °. 
Hab. Centrat Nicaragua: on the muddy margins of the Rio Tipitapa (Tate 7). 
The type was from the confines of Brazil and Bolivia, from Santa Ana de Chiquitos ?. 
It is not very probable that the Nicaraguan and Chiquitos shells belong to the same 
species, but I can give no more information beyond what is mentioned in the 
comparative table (anted, p. 539). 
Fam. CYRENIDA. 
[Gray (1840); Lamarck, Conchiféres fluviatiles (1819) ; Férussac, Cyclades (1821). | 
Bivalves with distinct anterior and posterior lateral teeth, and some smaller cardinals 
between them, usually of rounded or triangular outline, not much longer than high, 
without iridescent pearly appearance of the inside, generally of moderate or small size. 
Mantle open before, closed at the hinder part, with two distinct openings directed 
backward. 
POLYMESODA. 
Polymesoda, Rafinesque, Ann. gén. des Sciences Physiques, Bruxelles, 1820, pp. 287 et seq., and in 
Chenu’s Bibliotheque Conchyliologique, p. 27; Complete Writings of C. R. Rafinesque, ed. 
Binney and Tryon, p. 61 (1864) (as a subgenus of Cyclas, type Cyrena carolinensis, Bosc). 
More distinctly defined by Morch, in Malak. Blatt. vii. p. 193 (1860-61). 
Leptosiphon, Fischer, Manuel de Conch. p. 1000 (1872) (as a subgenus of Cyrena). 
Neocyrena, Fischer & Crosse, Miss. Scient. Mex., Moll. ii. p. 634 (1894). 
